PURPOSE: To eliminate the mutual direct interference between a modulating part and an oscillating part and to prevent the generation of the excitation of the waveguide mode, by screening the modulating part, the oscillating part, etc. independently of one another.

CONSTITUTION: The oscillating part and the modulating part are stored in respective cases 5 and 4 having a common wall 12, and the width of each cases 5 and 4 is made equal to or shorter than the half wavelength of the oscillation frequency. A notch is provided to a part of each of cases 5 and 4, and a dielectric resonator 1 is arranged so as to be coupled electromagnetically with an oscillation output line 2 and an induction line 3 through notches, and the resonator 1 is constituted so as to be covered with a resonator case 6 whose one side is equal to or shorter than the half wavelength of the oscillation frequency. Consequently, the direct coupling between the oscillating part and the modulating part and the excitation of the waveguide mode in cases 5 and 4 are prevented.