PURPOSE: To facilitate maintenance by memorizing the content of abnormality when the state of operation of a switch element is abnormal after a fixed time since the command for operation of the switch element is emitted.

CONSTITUTION: The commands S1WS4 for operation of a switch element are outputted to an output circuit 2 in response to stage advancing commands inputted to an input circuit 1 according to a programme previously stored in a memory circuit 10. After the time required for operating the switch element passes, the detecting codes D1WD4 of an input circuit 5 and the instruction codes of the output circuit 2 are compared, and the operation of output of the switch element is suspended when discordance is decided while each state signal is stored in a memory circuit 9. When an inspection command R is given to an input circuit 8, the contents stored in the memory circuit 9 are given to an annunciator 6 through an output circuit 7. Accordingly, the reliability is improved, and the maintenance can be facilitated.