To make the hardware and the software of the circuit in common to either of high active type and low active type signal input means.

In the case of using a high active switch 14, the switch is connected between an input terminal 13 and a power terminal (+B), and in the case of using a low active switch 15, the switch is connected between the input terminal 13 and a ground terminal GND. A microcomputer 16 inverts an output level of an active decision port Pout to switch on/off of two transistors(TRs) 21, 22 of the active decision circuit 19. When an input level to a signal input port Pin is changed before and after the switching, it is decided to be a switch off state and when the input level of the signal input port Pin is unchanged, it is decided to be a switch on state.