A mobile communication system is divided into a plurality of large zones, with each large zone being served by a large service area base station. The large zone is further divided into a plurality of small zones, each served by a respective one of a plurality of small service area base stations. Each base station broadcasts an identification signal for indicating a type of base station (i.e., large zone or small zone), and other necessary information relating to communication for notifying to the mobile terminal. The mobile terminal selects an optimum base station depending on certain conditions, such as the moving speed of the mobile terminal, the large zone or small zone where the mobile terminal being located, the signal receiving state from the base station currently communicating with the mobile terminal, and availability of the large zone or a small zone to be changed over by measuring signals received from other base stations.