PURPOSE: To attain mass production and to reduce the cost and the dispersion of frequency in a resonance circuit by integrating a 1st transistor(TR) into a resonance circuit and preparing a 2nd TR capable of acting its internal capacity as a circuit constant for regulating resonance frequency and outputting a resonance signal.

CONSTITUTION: A resonance circuit is constituted of a TR 11, capacitors 19 to 21 and a coil 13. The internal capacitance of the TR 11 is integrated into a circuit constant for determining the resonance frequency of the resonance circuit, the input capacitance is changed in accorance with a change in voltage VCNT to be applied to a collector and the resonance frequency is determined in accordance with the capcitance change. The resonance circuit is oscillated in accordance with the voltage VCNT to be applied, an oscillation current is allowed to flow into the base of a TR 12 in accorance with the oscillation, a current is allowed to flow into a collector based upon the oscillation current, and the capacitor 21 is charged with electricity through an emitter. Since the potential of the capacitor 20 is increased only by the charged capacitance of the capacity, a base current is furthermore allowed to flow and amplified by the TR 12 and the collector current is also increased and fed back to the base to hold resonance. Its resonance signal VOUT is outputted from the collector of the TR 12 through a capacitor 23.