To sharply reduce the in-board wiring for input and output of a signal with a facility/equipment outside a board via a terminal block from an in-board CPU unit.

Terminal blocks 11A and 11B mount serial transmission circuits, and serially transmit the signal input-output between them and a CPU unit 12. The CPU unit 12 is provided with one remote I/O board 12F for serial transmission. A parallel/serial mutual conversion circuit for input-output of a DI/DO signal and a digital/analog conversion circuit for input-output of an AI signal are mounted on the side of the terminal block. The terminal block is provided with a signal voltage converting circuit which converts the voltage of the input-output signal between itself and a facility/equipment. In case that the CPU unit is doubled, it includes such constitution that a serial transmission path is separated on the side of the terminal block and such constitution that an address setting switch is provided behind a nameplate. It includes such constitution that both sides of the terminal block can be used for wiring connection with the facility/equipment.