PURPOSE: To obtain the frequency stable over a wide temperature range and to realize miniaturization and low cost simultaneously.

CONSTITUTION: One terminal of, e.g. an AT-cut crystal vibrator 1 is connected to ground via a varactor element 2, the other terminal is connected to an oscillation amplifier circuit 3 to form a voltage controlled crystal oscillator 10. Resistor R1, R2, R3 are connected to a compensated voltage generating circuit at the side of a power supply V1 and thermosensing elements RT1, RT2, and RT3 are connected at the side of ground, and connecting points being a voltage division output section between the resistor R1, R2, R3 and the thermosensing elements RT1, RT2 and RT3 respectively are connected together via diodes D1, D2 to form a compensation circuit. Then the connecting point of the diodes D1 and D2 is connected to one terminal of the varactor element 2 being a component of the oscillator 10.