A mobile communication system for providing mobile communication service by radio to a mobile station is disclosed. The mobile communication system comprises base stations having a function of controlling hand-overs and in-coming and out-going calls necessary for providing the mobile communication service, and a multi-cell controlling station having a function of managing radio resources of plural base stations forming radio cells and selecting an optimum base station, and a function of allocating radio resources to the base stations. When at least one of the base station controls an in-coming or out-going call or controls a hand-over, if its own radio resource usage rate is lower than a threshold, the base station selects a base station to be allocated without communicating with the multi-cell controlling station.