PURPOSE: To obtain a circuit where the oscillation frequency is stable against temperature change without increment of current consumption, by cancelling transition of the oscillation frequency dependent upon temperature change by changing the power source voltage of the quartz oscillating circuit.

CONSTITUTION: At ambient temperature 20°C, variable resistor Rv of circuit DET is so adjusted that only the fifth stage of shift register SR of ambient temperature detecting circuit DET may be H. Under this state, the circuit is oscillated with a proper frequency by adjusting capacity Cg of voltage feedback circuit FB. Next, since the resistance value of thermistor TH of circuit DET is lowered when the temperature is lowered under this set state, the H signal in register SR is moved to the sixth or following stages. Therefore, the power source voltage becomes high which is applied to amplifying circuit AMP by ambient temperature/power source voltage converting circuit CONV, and the oscillation frequency is transferred to a higher one. When the ambient temperature is lower than 20°C, the H signal in register SR is moved to the fourth or following stages, and in this case, the power source voltage of circuit AMP becomes high also by circuit DET.