PURPOSE: To set stably an oscillation start voltage by supplying a voltage signal generated in a load resistor circuit to the 1st MOSFET gate electrode so as to control the drive power supply to the oscillation circuit.

CONSTITUTION: In taking the temperature characteristic of a resistor R2 and a FET 16 into consideration, the characteristic at the non-saturated region of the MOSFET is expressed in equation. The μeff is decreased as temperature rises and the resistance R2, in case of a P-channel semiconductor, increases as temperature rises. Thus, the relation of the temperature characteristic of the resistor R2 and the μeff cancels together according to equation and is not effected by the temperature fluctuation of the oscillation start voltage V0. Thus, the oscillation start voltage fed to the oscillation circuit has a temperature change, the voltage is set stably without being effected by the temperature change.