PURPOSE: To convert a high frequency into an easy-to-handle frequency while holding the phase between the voltage and the current of a transmission signal, by dividing both voltage and current cycle signals and changing the reactance of a matching means in response to the phase difference between both signals.

CONSTITUTION: A transmitter 1 is unmatched with an antenna 3 when an operating channel is switched. Therefore a phase difference is produced between the voltage and current cycle signals which are delivered from terminals 4a and 4b of a voltage/current detector 4 respectively. A voltage/current phase comparator 11 compares the phases of both signals and detect that the 2nd signal has a minus phase on the basis of the 1st signal. Therefore the output side of the comparator 11 is changed to L level from a high impedance. Then a motor 13 is reversed via a motor drive circuit 12, and a variable reactance element of a matching circuit 8 is controlled.