[Before the start of treatment period] - Children whose severity score calculated by the following formula on the basis of nasal symptom score (sneezing, rhinorrhea, nasal pruritus and nasal congestion) in the baseline assessment period (3 days from D5 to D7) is 10 or higher Severity of TNSS = [TDNSS(D-3)+TDNSS(D-2)+TDNSS(D-1)]/3