Provided are a group control radio base station and channel assignment method thereof. In a group control radio base station composed of a master base station and slave base stations, when the distribution of mobile stations is centralized in one, the probability of failure for the channel switch of the base station on one side of the distributed and centralized is high, and the circumstance thatthe call quality will keep difficult will happen. Each base station stores the number of vacant slots, under use or not-in-use of each slot, frequency carrier numbers, receiving level statuses of mobile stations in a resource judgment information table. The master base station receives link channel establishment request messages from the mobile stations and transmits resource confirmation requests of new messages to the slave base stations. The slave base stations receive the resource confirmation requests of the new messages and transmit stored information to the master base station by storing the information in resource confirmation replies. The master base station receives the resource confirmation replies of the new messages from the slave base stations and executes resource judgment processing. In the resource judgment processing, a radio base station suitable for a call base station of the group control radio base station is selected.