PURPOSE: To lower a required voltage by applying a bias to the driving stage of an output amplifying circuit so that the collector-emitter voltage of the transistor of the driving stage will be equal to that of the output stage.

CONSTITUTION: The constant voltage diode is split into constant voltage diode 21 and diode 22 and to their connection point, the collector of the transistor of the driving stage of the output amplifying circuit is connected. As a result, the collector- emitter voltage of the transistor of the driving stage becomes equal to that of the transistor of the output stage and the voltage overload point of the driving stage agrees with that of the output stage. Therefore, the voltage overload is determined by the driving stage and the collector-emitter voltage of the transistor of the output stage required to obtain the same voltage overload with the conventional circuit which needs the collector-emitter voltage of the transistor of the output stage about 0.7V more than that of the driving stage becomes about 0.7V lower.