PURPOSE: To resolve a problem of contact to cope with power up to a high power by selecting a minimum point of the current distribution of a quarter wavelength of the resonance frequency as the position of a fixed inner conductor and connecting it to a mobile inner conductor.

CONSTITUTION: A fixed inner conductor 1 of an inner conductor 11 is formed with dimensions corresponding to the 1/4 wavelength of the resonance frequency, and a mobile inner conductor 2 is formed with dimensions corresponding to the 3/4 wavelength of the resonance frequency. The conductor 2 is brought into contact with the conductor 1 by a finger 3 for connection. Then, the conductor 1 is placed at the point, where a current B does not flow on the distribution of the current B of the reentrant resonator, because the conductor 1 has dimensions corresponding to the 1/4 wavelength of the resonance frequency, and the conductor 1 is connected to the conductor 2 at this point by the finger 3. Consequently, a large current does not flow to the part of the finger 3. Thus, a problem of contact is resolved to cope with power up to a high power.