PURPOSE: To raise an apparent frequency accuracy in a temperature - frequency characteristic curve of a crystal resonator by biasing in the upper direction an apparent temperature characteristic by 1/2 of the maximum regulation.

CONSTITUTION: An oscillation frequency of a crystal resonator 11 is the highest at the time of a temperature T0, and becomes low as it separates from T0. An oscillating circuit 12 oscillates the resonator 11, a waveform shaping circuit 13 shapes an oscillation output wave in the shape of a pulse, a counting circuit 14 counts the most approximate value to 1/2 of a reciprocal of a regulation of the oscillation frequency varied in a peripheral temperature range for installing actually the resonator 11 with regard to the pulse, and after the counting, a carry signal is generated. Subsequently, a delaying circuit 16 generates one pulse caused by the carry signal, in the intermediate position of the pulse which has outputted this carry signal, an OR circuit 17 executes OR of output pulses of the circuits 16, 13, and a counting circuit 18 counts an output of the circuit 17 and outputs a pulse of a prescribed period.