PURPOSE: To make the circuit stable to temperature fluctuation by setting the current of the constant current source of a differential amplifier being one part of constitution of an oscillator, to be directly proportional to the thermal voltage of a transistor.

CONSTITUTION: An oscillation circuit 5, operational amplifier 6 and band gap regulator 7 are provided and this oscillation circuit 5 is composed of a differential amplifier 9 and a feedback circuit 8. A positive feedback signal is inputted to the base of a transistor Q3 and amplified by the differential amplifier 9 composed of transistors Q3 and Q4, and an oscillation signal is outputted from the collector of the transistor Q4 and positively fed back through coupling capacitors C6 and C5 to the base of the transistor Q3. The constant current source is composed of a transistor Q10 and an R7, and the current from this constant current source of the differential amplifier 9 is directly proportional to the thermal voltage of the transistor Q10. Thus, oscillation is enabled with a stable oscillation frequency against the temperature change.