PURPOSE: To prevent a direct current bias from being lowered by providing a bypass conducting path to the base resistance film for feedback amount attenuation of an oscillating path while connecting the central parts of both edges having the least high frequency current distribution.

CONSTITUTION: A base resistance film 2 for feedback amount attenuation is inserted to a conductive film 1 while exposing the lower resistance film by separating one part of the signal conductor film 1 of the oscillation path on a dielectric substrate 3, and the central parts at the edge parts of the separated conductor film 1 are connected by a conductor 5. Thus, no high frequency current almost passes through the connecting conductor 5, and it is operated only as the bypass conducting path for the direct current bias current.