To provide a communication system having a GPS receiver, where the transmission operation of a transmitter and a cellular phone does not affect the reception precision of GPSs, and to provide a method for controlling the communication system.

In the communication system that has the GPS receiver and transmits positioning data and other communication data from the GPS receiver, transmission by the transmitter is stopped while positioning data are being received by the GPS receiver, the communication system is set to a state so that it is capable of transmitting after the positioning data reception is completed, and the positioning data are transmitted.