PURPOSE: To make the pulse constant and to reduce the pulse interval by executing discharge of a charge in a capacitor forcibly through the use of a differential transistor(TR) and a constant current source.

CONSTITUTION: The charge in a capacitor 3 is discharged by a current I1 of a constant current source 6, voltages of points A, B are made equal and when a voltage VB at the point B is lower than a voltage VA at the point A, that is, when a voltage VD at the pint D is lower than a voltage VC at the point C, a differential amplifier Q1 is turned on, the charge in the capacitor 3 is discharged by a current I3 in a short time by the current (I1+I3). When the polarity of the voltage fed to input terminals 1, 2 is inverted, the capacitor is inverted in the opposite polarity again and the operation is repeated. Thus, the pulse width is set constant and the pulse width is decreased.