To easily investigate causes of a wrong alarm and a non-alarm by installing a monitoring microcomputer to monitor and process a first to a third signal information transferred between circuits in a sequence of generation of the signal information.

The monitoring microcomputer 14 monitors and processes the first signal information transferred between a receiving circuit 10 and a control circuit (central processing circuit) 11, the second signal information transferred between man-machine interface circuit 12 for operation and the control circuit 11 and the third signal information transferred between a man-machine interface circuit 13 for information and the control circuit 11 in the sequence of generation of the signal information. Specifically, when a change occurs in an input/ output part of the central processing circuit 11, the monitoring microcomputer 14 outputs analysis information on which change generating time data and the changing state data are combined to a storage device 15 in the sequence of generation. Consequently, even in a wrong alarm or a non-alarm whose causes are unknown, a range of investigation is narrowed to some extent, and the causes are easily investigated.