PURPOSE: To make a phase of an oscillating frequency stable with respect to a rapid surrounding temperature change.

CONSTITUTION: The oscillator is provided with an oscillation circuit 1 embeded, an insulator 2 covering spherically the circuit 1 with a large thermal resistance, and a conductor 3 with a small thermal resistance covering the outside of the insulator 2, then the temperature of the conductor changes uniformly due to a rapid change in the surrounding temperature and the temperature change is delivered gradually and uniformly to the oscillation circuit through the insulator to make the entire oscillation circuit to a uniform temperature gradually.