PURPOSE: To improve a productivity and to realize a mass production by controlling an input voltage of a temperature compensating circuit, varying a temperature output voltage characteristic of this temperature compensating circuit, and constituting so that a constant voltage is applied to a voltage capacity converting element in spite of magnitude of the input voltage at a prescribed temperature.

CONSTITUTION: In case when each variation quantity of an anode voltage variation quantity and a cathode voltage variation quantity of a variable capacity diode VD is equal, even if input voltage is varied, voltage applied to the variable capacity diode VD becomes constant, therefore, an oscillation frequency of a piezoelectric vibrator is not varied. A resistance value RT in a prescribed temperature of a temperature detecting part RT of a TCN 4 and a fixed resistance R is the same as a ratio RA/RB to RB, and accordingly, when Ra and Rb are selected so as to become a resistance ratio of a temperature compensating voltage generating circuit, even if input voltage applied to the TCN is varied at a prescribed temperature, voltage applied to the variable capacity diode VD becomes constant, and except the prescribed temperature, voltage based on a temperature output voltage characteristic is applied to the variable capacity diode VD.