PURPOSE: To prevent parasitic oscillation by controlling the oscillated output with a power supply voltage.

CONSTITUTION: A collector and a base of a transistor(TR) Q1 connect to a base of one terminal of a resistor R1 and a base of a TR Q2, the other end of the resistor R1 connects to a 1st power supply terminals 5 and an emitter of the TR Q1 and an emitter of the TR Q2 connect to a power terminal 7. Then a collector of the TR Q2 connects to one terminal of a constant current source 4 and a base of a TR Q3 and the emitter of the TR Q3 connects to the power terminal 7. Moreover, one terminal of the constant current source 4 connects to the terminal 5 and a collector of the TR Q3 connects to an output terminal of a crystal oscillation circuit. Thus, a parasitic oscillation caused before a time tTH when the power voltage V(t) reaches a voltage VTH starting the oscillation is not outputted and a desired crystal oscillation output is outputted at a time of t=tTH.