PURPOSE: To attain annunciation of occurrence of new fault even if the annunciation of a preceding fault is consecutive by monitoring a state of a fault taken place transited from a normal state to an abnormal state and annunciating the occurrence of a fault to the operator when the transition pattern is coincident with a preset check pattern.
CONSTITUTION: An output signal from a fault detection circuit 6 is inputted at a prescribed period and stored in a monitor state latch circuit 4. A check circuit 3 storing detection patterns discriminates whether or not the digital signal inputted to the monitor state latch circuit 4 is coincident with the check pattern signal. In the case of coincidence, it is discriminated that a disconnection fault of the circuit takes place and a high level signal representing 'fault occurrence signal' is outputted to a notice circuit 5. Thus, every time a fault takes place, the occurrence of fault is informed to the operator.