To provide a mobile communication system wherein bandwidth available for each of calls between a mobile communication terminal and a base station is changed according to a demand to the bandwidth during a call without exceeding a prescribed maximum level determined for the call.

A center distributes the bandwidth to mobile terminals and connects the mobile terminals to a ground network 22. A mobile terminal 2 is provided with a portable computer and executes a large number of various communication applications 4a, 4b, 4c, 4d. Driver software 6 that is executed in the mobile terminal 2 exchanges an API protocol to a protocol which is designed for a satellite communication system and capable of insisting on ownership. The mobile terminal 2 provides a physical interface I4 to an interface card 8 such as a PC (formally PCMICA) card. The interface card 8 includes a radio frequency modulator/demodulator connected to an antenna 10. The radio frequency modulator/demodulator receives a first frequency channel and simultaneously transmits it to a second frequency channel.