A thin and highly stable piezoelectric oscillator is provided with a piezoelectric vibrator, a mother printed board which supports a piezoelectric vibrator main body on its one face and connects lead terminals to a wiring pattern, oscillating circuit parts which are mounted on one face of the mother printed board to be disposed in close contact with one face of the piezoelectric vibrator main body, adjusting circuit parts which are mounted on the other face of the mother printed board, an internal printed board which is provided in contact with the other face of the piezoelectric vibrator main body, and heater resistors which are mounted on the internal printed board to be disposed in close contact with the other face of the piezoelectric vibrator main body. Thus, since such a configuration is employed that, while the oscillating circuit parts mounted on the mother printed board are brought in close contact with the one face of a metal case of the piezoelectric vibrator, the heater resistors mounted on the flexible printed board are brought in close contact with the other face of the metal case for the piezoelectric vibrator, not only the heater resistors heat the piezoelectric vibrator but also it indirectly heats the oscillating circuit parts efficiently.