 aspect of the present invention, there is provided an electronic musical instrument comprising: a delay time extracting means for storing a plurality of first delay times comprising a period that changes depending on a sounding volume and is a period after execution of a sound-producing instruction until generation of a string-striking sound and a plurality of second delay times comprising a period that changes depending on the sounding volume and is a period after execution of the sound-producing instruction until generation of a shelf board impulsive sound, and extracting a first delay time and a second delay time corresponding to a sounding volume specified by a sound-producing instruction operation from among the stored plurality of first delay times and second delay times; and a musical tone generating means for generating the string-striking sound having a pitch specified by the sound-producing instruction operation when the first delay time extracted by the delay time extracting means has elapsed after execution of the sound-producing instruction, generating the shelf board impulsive sound when the second delay time extracted by the delay time extracting means has elapsed, and generating a musical tone having a combination of the generated string-striking sound and the shelf board impulsive sound. In accordance with another aspect of the present invention, there is provided an electronic musical instrument comprising: a delay characteristics storing means for storing a plurality of first delay times comprising a period that changes depending on a key-pressing strength and is a period after execution of a key press until generation of a string-striking sound and a plurality of second delay times comprising a period that changes depending on the key-pressing strength and is a period after pressing a key until generation of a shelf board impulsive sound; an extracting means for extracting a first delay time and a second delay time corresponding to a key-pressing strength generated by a key-pressing operation from the delay characteristics storing means; a string-striking sound generating means for generating the string-striking sound having a pitch depending on the key-pressing operation when the first delay time extracted by the extracting means has elapsed after pressing the key; a shelf board impulsive sound generating means for generating the shelf board impulsive sound when the second delay time extracted by the extracting means has elapsed after pressing the key; and a musical tone generating means for generating a musical tone having added thereto the string-striking sound generated by the string-striking sound generating means and the shelf board impulsive sound generated by the shelf board impulsive sound generating means. In accordance with another aspect of the present invention, there is provided an electronic musical instrument comprising: a delay characteristics storing means for storing a plurality of types of delay characteristics having a plurality of first delay times comprising a period that changes depending on a key-pressing strength and is a period after execution of a key press until generation of a string-striking sound and a plurality of second delay times comprising a period that changes depending on the key-pressing strength and is a period after pressing the key until generation of a shelf board impulsive sound; a selecting means for selecting any of the plurality of types of delay characteristics stored in the delay characteristics storing means; an extracting means for extracting a first delay time and a second delay time corresponding to a key-pressing strength generated by a key-pressing operation from the delay characteristics storing means within the delay characteristics selected from the delay characteristics storing means by the selecting means; a string-striking sound generating means for generating the string-striking sound having a pitch depending on the key-pressing operation when the first delay time extracted by the extracting means has elapsed after pressing the key; a shelf board impulsive sound generating means for generating the shelf board impulsive sound when the second delay time extracted by the extracting means has elapsed after pressing the key; and a musical tone generating means for generating a musical tone having added thereto the string-striking sound generated by the string-striking sound generating means and the shelf board impulsive sound generated by the shelf board impulsive sound generating means. In accordance with another aspect of the present invention, there is provided a computer program product for an electronic musical instrument stored on a computer-readable medium and executed by a computer, comprising the steps of: a delay time extracting process for storing a plurality of first delay times comprising a period that changes depending on a sounding volume and is a period after execution of a sound-producing instruction until generation of a string-striking sound and a plurality of second delay times comprising a period that changes depending on the sounding volume and is a period after execution of the sound-producing instruction until generation of a shelf board impulsive sound, and extracting a first delay time and a second delay time corresponding to a sounding volume specified by a sound-producing instruction operation from among the stored plurality of first delay times and second delay times; and a musical tone generating process for generating the string-striking sound having a pitch specified by the sound-producing instruction operation when the first delay time extracted by the delay time extracting means has elapsed after execution of the sound-producing instruction, generating the shelf board impulsive sound when the second delay time extracted by the delay time extracting process has elapsed, and generating a musical tone having a combination of the generated string-striking sound and the shelf board impulsive sound. In accordance with another aspect of the present invention, there is provided a computer program product for an electronic musical instrument stored on a computer-readable medium and executed by a computer, comprising the steps of: an extracting process for storing a plurality of first delay times comprising a period that changes depending on a key-pressing strength and is a period after is a period after execution of a key press until generation of a string-striking sound and a plurality of second delay times comprising a period that changes depending on the key-pressing strength and is a period after pressing a key until generation of a shelf board impulsive sound, and extracting a first delay time and a second delay time corresponding to a key-pressing strength generated by a key-pressing operation from among the stored plurality of first delay times and second delay times; a string-striking sound generating process for generating the string-striking sound having a pitch depending on the key-pressing operation when the first delay time extracted by the extracting process has elapsed after pressing the key; a shelf board impulsive sound generating process for generating the shelf board impulsive sound when the second delay time extracted by the extracting process has elapsed after pressing the key; and a musical tone generating process for generating a musical tone having added thereto the string-striking sound generated by the string-striking sound generating process and the shelf board impulsive sound generated by the shelf board impulsive sound generating process. In accordance with another aspect of the present invention, there is provided a computer program product for an electronic musical instrument stored on a computer-readable medium and executed by a computer, comprising the steps of: a selecting process for storing a plurality of types of delay characteristics having a plurality of first delay times comprising a period that changes depending on a key-pressing strength and is a period after execution of a key press until generation of a string-striking sound and a plurality of second delay times comprising a period that changes depending on the key-pressing strength and is a period after pressing the key until generation of a shelf board impulsive sound, and selecting any of the plurality of types of delay characteristics; an extracting process for extracting a first delay time and a second delay time corresponding to a key-pressing strength generated by a key-pressing operation from within the delay characteristics selected in the selecting process; a string-striking sound generating process for generating the string-striking sound having a pitch depending on the key-pressing operation when the first delay time extracted by the extracting process has elapsed after pressing the key; a shelf board impulsive sound generating process for generating the shelf board impulsive sound when the second delay time extracted by the extracting process has elapsed after pressing the key; and a musical tone generating process for generating a musical tone having added thereto the string-striking sound generated by the string-striking sound generating process and the shelf board impulsive sound generated by the shelf board impulsive sound generating process. 