PURPOSE: To accurately and easily adjust an initial resonance frequency.

CONSTITUTION: Plural holes 4 with bottom for frequency adjustment are provided on a resonator section 1, and a frequency adjusting member 5 consisting of the same dielectric material as or equivalent to that of the resonator section 1 is sequentially inserted to each frequency adjustment hole 4 with bottom to adjust the deviation of the frequency from a setting resonance frequency while measuring the resonance frequency of the dielectric resonator. Moreover, an alumina may be also used for the material of the frequency adjustment member used for fine adjustment. The size of the material used for the fine adjustment may be smaller than the material used for rough adjustment.