PURPOSE: To keep distortion lower to a wide range of transmission frequency by controlling a distortion generator for correcting intermodulation distortion with a control signal controlling an output frequency of a local oscillator.

CONSTITUTION: A linearizer 6 branches an intermediate frequency signal inputted from an input terminal 11 into two, the 1st and 2nd intermediate frequency signals; a distortion is given to one signal by the distortion generating circuit 9 and also the other intermediate frequency is subjected to phase adjustment through a delay circuit 8. An output signal of a variable phase shift circuit 13 and a variable attenuation circuit 14 by using a control signal of a control circuit 12 to change an output frequency of the synthesizer type local oscillator 5. Both the signals are applied to a synthesizer 7, where they are synthesized and the result is applied to a high output amplifier 2 via a mixer 4. Thus, the intermodulation distortion generated by the high output amplifier 2 is improved.