When a base station stops transmission due to its maintenance, transmission electric power of the base station is controlled so that a radio network between a mobile station and a selected one of the mobile station and the neighboring stations may not be disconnected. The base station gradually reduces the level of transmission electric power. Until the transmission completely stops, soft handoff deletion procedure between the base station and the mobile station is performed and soft handoff addition procedure between one of the neighboring base stations and the mobile station is performed.