The Bereitschaftspotential (BP), event related synchronization (ERS) and event related dysynchronization (ERD) will be analyzed for the investigation of the possible differences of brain activities prior to leg voluntary movement between patients and controls. In addition, the synchronized recorded gait parameters for gait ignition,turning and termination will also be analyzed. The information gathered will allow us to further understand the pathophysiology of the gait freezing in PD. Investigators will deliver a course of rTMS with intermittent theta burst paradigm of the leg motor cortex to investigate whether the non-invasive brain stimulation can ameliorate the gait freezing in PD patients. The subjects will be assessed before and 4 times after rTMS during an 8-week period with clinical scoring batteries and electrophysiological recording as aforementioned. At the end of the 8th week, the test group and sham group will cross over and undergo the same procedures as aforementioned. The serial comprehensive investigations in this project will not only promote our understanding of the gait freezing pathophysiology but also may charge a novel trail for the management of long suffering symptom of the PD patients.