1. A data communication system comprising: a first mobile unit having first transmission/reception means for transmitting a first request signal containing position information to a base station and receiving data corresponding to the first request signal from the base station; a base station having search means for searching for a second mobile unit in accordance with the position information contained in the first request signal, and second transmission/reception means for receiving the first request signal, transmitting a second request signal to the second mobile unit thus searched for, and returning data returned from the second mobile unit to the first mobile unit; and a second mobile unit having input means for inputting data, and third transmission/reception means for receiving the second request signal and returning the data inputted by the input means in accordance with the second request signal to the base station.