To provide a mobile communication system used for the purpose of supplementation of areas of ground cellular that can ensure traffic capacity of areas in which only satellite communication is available.

The mobile communication system is provided with a mobile communication service controller 7 including a home location register 9 that is connected to a ground cellular network and a mobile satellite communication network to manage location information and telephone numbers of mobile devices and a memory 10 that stores ground cellular area information, the system has a network operating modes of a ground cellular out-area priority mode where the satellite communication mode takes precedence at the outside of the ground cellular area and an ordinary mode where full spot beams are available without the priority mode, a mobile satellite communication channel control station 4 in the ground cellular out-area priority mode discriminates the availability of each spot beam of a communication satellite via a satellite communication base station 5 on the basis of the area information in the ground cellular area information memory and does not allocate the satellite spot beam to the area available of the ground cellular communication as its control.