PURPOSE: To simplify a power source control procedure for hot-line insertion and extraction by providing an input/output control module with a function which controls the power source of an input/output device under its control.

CONSTITUTION: A power source control means 10 judges which of the control signal for the insertion of the module and the control signal for the extraction is received, when receiving an insertion/extraction control signal from an insertion/extraction control part 9, and when it is judged to be the control signal for the extraction, the IOC module power source control part of the power source control means 10 sends out a power-off control signal to an I/O bus power source control part. Then the I/O bus power source control part sends out a power-off signal to a photocoupler 13, which varies in the logical level on the side of an I/O power source control line 14, and, an I/O power source 8 stops supplying electric power to respective I/O device power sources 8a, 8b, and 8c. When the insertion/extraction control signal is the control signal for the insertion, the IOC module power source part turns on a module power source 5c and sends out a power-on control signal to the I/O bus power source control part.