PURPOSE: To supply a sufficient driving current to the input electrode of an output stage transistor(TR) and to prevent a sag in an output pulse even when a pulse period is long by connecting a resistor between clamp points of 1st and 2nd clamp circuits.

CONSTITUTION: A 1st stage TR QA is on/off-controlled in response to an input pulse Si fed to an input terminal IN. With the TR QA turned off, a 1st diode D1 is used to clamp the clamp point P1 of a 1st clamp circuit CL1 to a low level. Moreover, with the TR QA turned off, a 2nd diode D2 is used to clamp point P2 of a 2nd clamp circuit CL2 to a low level. With the TR QA turned on, a charge in a capacitor C2 is fed to the input electrode (base) of a TR QB through a resistor RB, In such a case, a sag is eliminated from an output pulse by selecting a time constant comprising the 2nd capacitor C2 and the resistor RB larger than a time constant comprising the 1st capacitor C1 and an emitter dynamic impedance of the output stage TR QB.