PURPOSE: To execute efficient and stable operation by matching impedance based on a reflection coefficient calculated from a progressive and a reflected wave detected from a power fed to a transmission antenna even with the transmission antenna having a low antenna height and whose grounding is incomplete.

CONSTITUTION: When a power from a communication equipment is fed to a feeding point 18, matching devices 21∼23 match the input impedance of an antenna 15. The reflected wave from the feeding point 18 is fed to a directional coupler 24 via a matching device 25 and the progressive wave being the transmission power is fed to the antenna 15 via the matching device 25 from the directional coupler 24. The directional coupler 24 extracts separately a part of the progressive wave and the reflected wave respectively out of the power and transmits the result to an AD converter 27 via a prreamplifier 26. A CPU28 calculates the reflecting coefficient of the antenna 15 from each signal of the progressive wave and the reflected wave being digital quantity, changes the reactance of the matching device 25 by driving a motor M1 or M2 based on the calculated reflection coefficient so as to match the impedance.