PURPOSE: To always obtain a sufficient radiation efficiency by interposing an automatic matching device detecting an antenna input impedance and matching it with an output impedance of a transmitter with a transmitter feeding a signal to an antenna main body so as to constitute the titled system in a way that the matching condition is varied with the fluctuation of the radiation resistance.

CONSTITUTION: A tower 11 is made up of a cylindrical pipe, an iron tower truss support and an FRP coated with a conductive material or the like, and the tower is stood on the ground 12 via an insulator 21 at the base at a height (h) of,e.g., 1/2 λ. Then the matching device comprising two detectors 28, 29 and an automatic matching device 30 is interposed and connected between the feeding part at the lower end of the tower 11 and the transmitter 27. In the automatic matching device, the antenna input impedance is always monitored by the detectors 28, 29 and a correction signal with respect to a matching coil L and a matching capacitor C in response to the quantity of change is fed back to the automatic matching device 30 to always attain the matching with the output impedance of the transmitter 27.