PURPOSE: To increase the current consumption by using a high speed switching transistor (Tr) when an output Tr of a power amplifier is turned off so as to bring the base potential forcibly to nearly zero thereby inhibiting a collector current from flowing.

CONSTITUTION: The power amplifier consists of Trs 5, 6 and an output Tr4. When a position period portion of an input signal is fed to the Tr6, the Tr5 is turned off by a control signal fed to the base. On the other hand, when a negative portion of the input signal is fed to the Tr6, the Tr5 is turned on by a control signal fed to the base and a base-emitter voltage of the Tr6 is brought forcibly to nearly zero. As a result, the collector current flowing when the input signal is at a negative period portion is nearly zero and the increase in the current consumption is suppressed.