PURPOSE: To employ a conventional power supply without use of a stabilized power supply as a power supply for the amplifier circuit.

CONSTITUTION: An impedance (-Zr) connected in series with an internal impedance (Zr) of a power supply 3 and an impedance Zc1 (or Zc2) of an output stage transistor(TR) is provided to the amplifier circuit 1 and in order to select a monitoring point of the impedance (-Zr) to be an earth point of a load similarly to the case with that of a stabilized power supply, an arm of the said amplifier circuit 1 is in one-point connection to the earth of the load.