PURPOSE: To provide more efficient channel segregation by changing the priority of a channel corresponding to the presence/absence of channel allocation based on plural threshold levels and the priority with respect to a carrier power/ interference wave power ratio (CIR).

CONSTITUTION: Each channel CIR is measured and the priority of the channel is changed in accordance with the presence/absence of channel allocation based on the measured result and the priority. Namely, the priority is updated as follows: (1) When the CIR measured at a certain channel is a first threshold value or less, the priority of the channel is decreased. (2) When the measured CIR is within the range an n-th threshold level or above and an (n+1)th threshold level or below (wherein, n is an integer between 1 and N-1), the priority is increased/decreased just by the prescribed leve. (3) When the measured CIR is in the CIR area more than an N-th threshold level, the priority is not changed. (4) When the channel is allocated based on the priority, the priority of the channel is increased.