PURPOSE: To stably start up oscillation by detecting no output from a voltage control oscillator, increasing the amplification factor of an amplification part in the voltage control oscillator and supplying a clock pulse from a clock gener ating circuit to a function generating part.

CONSTITUTION: When the impedance CI of a piezoelectric element is increased by a change with the passage of time or the like, the oscillation of the voltage control oscillator 5 is suspended. Since no signal is outputted to the output terminal of a frequency dividing circuit 6, a clock signal CK to the function generating circuit 3 is switched to a clock pulse from a clock generating circuit 7 through a switching circuit 9 and a switching control circuit 8 and the amplifi cation factor of the amplification part in the oscillator 5 is increased. Since the oscillation of the oscillator 5 is started up by the increment of the amplifica tion factor, the switching circuit 9 supplies the signal from the circuit 6 to the circuit 3 as the clock signal CK to execute oscillation control based upon a prescribed feedback loop.