PURPOSE: To stabilize the initial operation of the computer system using, for example, an interface of the SCSI system by providing the function, which turning on/off a private power source on the target side in accordance with turning-on/off of a system power source on the initiator side, to approximately equalize the start timing of the initiator and that of the target.

CONSTITUTION: In the interface device of, for example, the SCSI system where an initiator 1 and a target 2 are connected, a power source remote circuit 14 provided in the target 2 switches a private power source 11 to the turning-on operation in accordance with an input voltage corresponding to the high level of the control voltage, which is outputted at the time of the turning-on operation of a system power source 5, and switches it to the turning-off operation in accordance with an input voltage corresponding to the low level of this control voltage. A reset IC 19 keeps the input voltage level corresponding to the low level of the control voltage.