PURPOSE: To obtain an output pulse at a preset level or over even when the received pulse width is short by providing a pulse providing circuit started by a signal at an output terminal and resetting a pulse detection circuit after a prescribed time and compensating the distortion of pulse the to a chattering erasing circuit by the said pulse provision circuit.

CONSTITUTION: The pulse provision circuit 5 resets the pulse detection circuit on the condition that the input signal is at an L level with a prescribed time after the tip of an H level when the signal at an output terminal 4 is at an H level. When the input signal is at the H level after a prescribed time, the pulse detection circuit 2 is not reset but reset when the input signal is at an L level. Thus, the pulse provision circuit 5 compensates the pulse distortion due to the chattering erase circuit 3 regardless of chattering in the input signal to offer an output with a prescribed pulse width.