An object of the present invention is to avoid communication congestion by varying the transmission times of a plurality of mobile bodies while maintaining standardization in the software to be installed in the plurality of mobile bodies. A detection is made in a plurality of vehicles 31, 32, 33 . . . that a specific event has occurred in a vehicle, for example a communication terminal 56 has been installed, or in other words power from a power source 63 has been applied to the communication terminal 56. The power application time is then measured by a calendar and timer in the interior of the vehicle. An individual automatic transmission time for each vehicle is then set with the power application time of the vehicle as a reference.