In a mobile communication system, which has a plurality of radio network controllers and a number of radio base stations connected to each of the radio network controllers, for sending and receiving user data between a host network and mobile stations via the radio network controllers and radio base stations, a plurality of transmission paths that pass through one or more radio network controllers are set up between a base station, which sends and receives radio signals to and from a mobile station, and the host network. When data is being sent and received using one transmission path from the host network to a base station through a radio network controller, traffic conditions on this transmission path are monitored. When traffic has increased, the user data is dispersed by being passed through a plurality of transmission paths.