nullObject of the inventionnull To provide designing means that prevents deterioration through thermal aging of an electronic part used in high-stability piezoelectric oscillators and the like when the high end of the usage temperature is 85 deg C. nullMeans for solving the problemnull In a high-stability piezoelectric oscillator equipped with: a first isothermic oven housing a piezoelectric vibrator and an electronic part; a second isothermic oven; a case; and the like, a high-stability piezoelectric oscillator wherein a temperature of the first isothermic oven is set to be lower than a temperature of a second isothermic oven using a Peltier element or the like.