To attain stable data transmission by avoiding a reduction of a data processing efficiency in a station conducting data processing.

In the data transmission system where data transmission is conducted between a central station and plural base stations in star connection with the central station via full duplex data channels 21, 22 in two-way, when a data transmission/reception processing section 31 processes incoming and outgoing data between the central station and the base stations, a buffer 32 stores unprocessed data of received data, a buffer monitor section 33 monitors the operating state of the buffer 32 to detect an increase of the data storage amount and an increase of the data processing load. Based on a detected result from the buffer monitor section 33, a channel control section 34 controls a band width of the data channels 21, 22 to make a band of an incoming data channel between the central station and the base station narrower and to extend a band of an outgoing data channel at the time of congestion of burst data transmission between the central station and the base stations.