To enable even the monitoring of an analog circuit part by comparing digital data inputted from analog circuit parts connecting with respective CPUs after A/D conversion in a process wherein the two CPU monitors their operations mutually.

Signals inputted from analog circuit parts such as an operational amplifier 5 and an A/D conversion part 3 or an operational amplifier 6 and an A/D conversion part 4, etc., to a CPU 1 and a CPU 2 by branching an analog signal are classified by levels by a level classifying means and converted by an analog monitor signal generation part into analog monitor signals T1, T2, and T3; and the frequency or pulse width of the analog monitor signal generated by the CPU 1 or 2 is compared with that of the analog monitor signal inputted from the CPU 2 or 1 and it is decided that the analog circuit part is normal when they match each other or abnormal when not.