There is provided a high-stability piezoelectric oscillator. The high-stability piezoelectric oscillator includes an oscillating circuit unit that has a piezoelectric vibrator and oscillating circuit components, an inner oven that accommodates the oscillating circuit unit, an outer oven that accommodates the inner oven, and an outer metallic case that covers the outer oven. Further, airtightness is ensured inside and outside the outer metallic case. Furthermore, at least one of the outer oven and the inner oven is airtightly sealed.