PURPOSE: To attain rapid operation, to simplify constitution and to reduce a deviation in the duty ratio of an input and an output.

CONSTITUTION: The cathode side terminal of a serial connection between two diodes D1, D2, one terminal of a resistor R1 and one terminal of a resistor R2 are connected to the base of an npn type transistor(TR) Q1, the anode side terminal of the diodes D1, D2 serially connected to the collector of the TR Q1 and the other terminal of the resistor R2 are connected to a high potential side power supply line VCC and the emitter of the TR Q1 is connected to a low potential side power supply line VSS through a resistor or a constant current source A.