PURPOSE: To eliminate the non-requested signal such as the noise or the like and to detect the requested signal only, by making the timer start counting simultaneously with the start of the input signal, delivering the output by the counting of the setting time and giving resetting halfway with application of the stop signal.

CONSTITUTION: The interruption request signal supplied to terminal 1 undergoes waveform shaping 3 and is supplied to start signal generator gate circuit 9 and stop signal generator gate circuit 10. The start signal is produced in response to the start of the ihput signal, and the stop signal is generated in accordance with end of the input signal. The output of circuit 9 and 10 are led to the timer 13, and the set time counting is started by the start signal of circuit 9 and the output is delivered through the output terminal in accordance with end of the time counting. When the stop signal of circuit 10 is supplied within the set time, the counting is stopped and the resetting is given to the initial value. As a result, the non-requested signals such as the noise or the like can be eliminated, and only the requested signals can be detected