PURPOSE: To carry out the temperature compensation of oscillating frequency of a reference oscillator by employing change of oscillating frequency due to temperature of a ring oscillator in which odd steps of MOS inverters longitudinally connected continuously.

CONSTITUTION: The difference between the frequency of a ring oscillator 1 in which an oscillating frequency can be adjusted by a capacitor 2 and the frequency of a crystal oscillating circuit 4 is inputted to a frequency dividing circuit 11 and AND gate 10. A timer 12 is triggered by the output of the frequency dividing circuit 11, AND gate 10 is opened by a predetermined time t necessary for the temperature correction of the crystal oscillator, and the frequency difference between the crystal oscillating circuit 4 and the ring oscillator 1 is inputted to a pulse inserting circuit 7 as interruption pulse PI. In the pulse inserting circuit 7, OR of differentiating wave shape of rise or fall of the interruption pulse and output Mo of a frequency divider 5 is taken. This output is frequency divided 8 and time displayed 9.