To efficiently save power as to a power supply control system for connecting/disconnecting the supply of driving power adaptively to a signal sequence with respect to a line terminating set (DCE) or a data terminal device (DTE) to which a DTE/DCE interface is applied.

The power supply control system is provided with a connection control means 11 connected to an opposite device through a DTE/DCE interface and capable of transmitting/receiving a hand-shake signal related to both or one of the setting and release of physical connection to be formed between the means 11 itself and the connected device, a power supply circuit 12 for discriminating whether there is transmission information to be transmitted to the device or not, and only when the discrimination result is true, supplying power and a transmission means 13 for receiving a part of all of driving power supplied by the means 12 as power and transmitting transmission information to the device through the DTE/DCE interface.