PURPOSE: To attain ease of adjustment of oscillated output and also to widen the variable range of an oscillating frequency by covering a dielectric resonator with a conductive substance having a hole for electromagnetic coupling and providing a mechanism adjusting a volume of an accommodated space of the dielectric resonator to the conductive substance.

CONSTITUTION: A cylindrical metallic case 14 possible for adjusting the inner volume coverting the dielectric resonator 8 is provided. A frequency adjusting screw 15 is provided at an upper part of the cylindrical metallic case 14, the inner volume of the cylindrical metallic case 14 is changed by turning the screw and changes the frequency by giving an effect on the magnetic flux distribution surrounding the dielectric resonator 8. Two coupling windows 16 are provided to the case 14 so as to obtain the coupling to the resonator 8 and the microstrip lines 2, 3. In an example of this execution, since the effect of external conditions is hardly susceptible, the adjustment of frequency or the like is conducted easily by removing a metallic case cover 11. Further, the oscillated output is varied depending on the size of the coupling windows 16.