PURPOSE: To establish the voltage controlled crystal oscillation stabilizing the oscillated frequency, by mutually cancelling the change in the frequency produced with the variation of parameter of the circuit element due to the variation of the power supply voltage.

CONSTITUTION: The oscillation of the third order over-tone oscillation mode of the crystal oscillator Q1 is made with the Colpitts oscillation circuit having the transistor TR1, Zener diode ZD1, resistor R2, capacitor C3, inductance L1 and basic capacitors C1, C2. The inductance Ls stabilizes the oscillation circuit as known as the method of levering, and the value is a value shifted slightly from the essential optimal value. As a result, the excitation circuit including the transistor TR1 produces the frequency shift with the variation of the power supply voltage Vcc, and this shift is cancelled with the frequency shift with the simple stable bias circuit by means of the Zener diode ZD1.