PURPOSE: To provide a power supply controller for PWBA which can save electric power by independently deciding a standby state without receiving any instruction from a central control processor.

CONSTITUTION: A power supply control circuit 2 judges whether or not a host device designates its own PWBA from a control signal 13 sent from the host device and, when the circuit judges that its own PWBA is designated, initializes a control circuit 4 by outputting an initial signal 7 to the circuit 4 and, at the same time, turns on a power switch 3. The control circuit 2, in addition, sends the data 12 and control signal 13 sent to its own PWBA to the control circuit 4 after once fetching the data 12 and signal 13 by means of a latch, etc. The control circuit 4 performs such actual processing as the development of the received picture data into image data, etc. In addition, the circuit 4 outputs a power supply interrupting signal 6 to the control circuit 2 when the circuit 4 starts idling. Therefore, the power supply to the circuit 4 is interrupted or reduced while the circuit 4 is in an idling state and the power consumption of the circuit 4 can be reduced.