PURPOSE: To realize a stable temperature compensation oscillator against a transient temperature fluctuation 3 as well by sealing an oscillator main body to a low thermal resistance substance.

CONSTITUTION: The entire part of a direct temperature compensation oscillator 5 having a thermosensing element 1 and electric components 2, 3 mounted on a printed circuit board 4 in its oscillation circuit is sealed in a low thermal resistance substance 6. Thus, no air convection is present between the thermosensing element 1 and the other electric components 2, 3 of the direct temperature compensation oscillator 5 and the temperature difference is kept always 1°C or below, then even when the transient temperature fluctuation element is located at the outside of the direct temperature compensation oscillator 5, the temperature is compensated. Thus, the frequency stability of the direct temperature compensation oscillator is improved against the transient fluctuation of the temperature.