PURPOSE: To attain the oscillation at a low power supply voltage by connecting any gate of two P-channel and N-channel MOS transistors(TRs) provided to an oscillation section to a constant voltage source.

CONSTITUTION: A source of an N-channel MOS transistor(TR) (N-MOSTR)6 connects to ground and its drain connects to a drain of a P-MOSTR 4. Then the source of the TR 4 connects to a VDD 2 and the drain connects to one terminal of a resistor 9 and one terminal of a crystal oscillator 1, and the other terminal of the resistor 9 and the other terminal of the crystal vibrator are connected together. Then the oscillation circuit is obtained by connecting a low voltage power supply 10 to any gate of the TRs 4, 6 or the gate of the other TR. For example, the gate of the TR 4 of the oscillation section is connected to a constant voltage source 10 and the voltage of the constant voltage source is set to be VGSP≥VTP, and the power supply voltage is reduced more than that of a circuit whose VDSP is set larger than VTP by the selection of the size of TRs, where VGSP is a gate-source voltage of the TR4, VTP is a threshold level and VDSP is a drain-source voltage.