PURPOSE: To improve the frequency characteristic without gain reduction by increasing a conductance of a load transistor(TR) for an invalid period of a signal voltage of an impedance converter processing an input signal having a valid period and an invalid period alternately so as to increase a discharge current.

CONSTITUTION: A voltage from a constant voltage power supply 107 is impressed to a charge absorbing terminal of a drive TR 101, and output terminals of a charge supply terminal of the TR 101 and a charge absorbing terminal of a load TR 102 are used for a signal output section 106. A voltage of a clocked power supply 108 is impressed to the charge supply terminal of the TR 102. A prescribed control voltage is impressed to a load control input section 105 of the TR 102. The voltage of the power supply 108 is changed for a prescribed period in a potential to control charge supply quantity to the output section 106.