A mobile unit information sharing system with which it is possible by wireless communications and without providing a communications control station to share not only voice data but also position information of multiple mobile stations and business information such as images formed in the course of business and instructions and the like. A base station and multiple mobile stations each, by a time-sharing synchronous wireless modem device, acquire position information for themselves and time information via a GPS antenna and transmit their station position information via a wireless installation using a wireless frequency common to all the stations and with timing determined, on the basis of the acquired time information, so that their station position information does not collide with position information transmissions from other stations.