PURPOSE: To make the change in a set value of an oscillating frequency easy and to improve the mass-productivity of an operating shield case, by standardizing the side of the other shield part except a conductor base forming the oscillator.

CONSTITUTION: A shield case is formed with a shield side wall conductor 11 formed into the standard size so that the inside surrounded with the side surfaces has a predetermined volume, a conductor base 12 formed to be inserted from the bottom to the inside, and a conductor cover 13. The upper part of the conductor is mounted with the oscillator comprising a semiconductor element, a dielectric resonator 14, and circuits connecting them. The thickness of the part inserted to the inside of the side wall conductor of the base 12 is selected in response to the frequency band of the oscillator, allowing to eliminate the effect of unnecessary resonance mode.