To enable to make a data transmission between a base station and a terminal station at a low cost.

In a data transmission system 1 comprising a terminal station 10 and a base station 30 to perform data exchange through a communication network, the station 10 has a first switching control section 12 for controlling a communication direction to switch it to a single direction and a management center 30 has a second switching control section 33 having the same function. Both sections 12 and 33 synchronize a communication direction by control signals SW1 and SW3 transmitted from one side to the other to control it by switching. In this way, large capacity image data, etc., can be transmitted from the station 10 to a transmitted data storing section 34 in the management center 30 in a short time to store the data. Further, the data stored in the section 34 can be transferred (fed back) to the station 10.