To suppress the variation of a main signal component and to stably reduce distortion by generating distortion by connecting a wide band small power amplifier to the first output of a third power distributor for distributing power to three systems, providing only a distortion signal by subtracting distortion from a second output and removing the main signal component, and supplying the distortion signal, in which the main signal component and a main signal are not included, to a main amplifier by adding the distortion signal with a third output.

The distortion signal, from which the main signal component is removed, is added with an input signal by a second power synthesizer 30. The distortion signal is of the power level of one to the component of a gain to the distortion signal generated by a main amplifier 13 connected to the output of the second power synthesizer 30, and the amplitude and the phase are controlled by a second vector controller 51 so as to provide opposite phases. Besides, since the main amplifier 13 is in a linear operating area in respect to the level of the distortion signal injected to the input of the main amplifier 13, the distortion of the main amplifier 13 becomes an extremely small value in respect to the injected distortion signal and the distortion signal to be generated by the main amplifier 13 is generated only by the main signal component.