PURPOSE: To enable an impedance converter circuit to correspond to a load of any capacity by a single signal source by flowing a constant current through an impedance circuit all the time by bearing complementary relation between a load current flowing through a load circuit and a current flowing through an active element.

CONSTITUTION: A current applied to load circuit 8 from signal source 6 flows to even impedance circuit 9 to cause variation in potential across it. As a result, the base-emitter potential of transistor 10 varies and its emitter current changes so as to cover variation in signal current. As a result, variation in protential due to the signal current of impdeance circuit 9 is canceled by an emitter current varying according to variation in this potential.