A Colpitts oscillator has an integrated circuit. The integrated circuit includes a transistor having an equivalent large size, a bypass capacitor connected between a collector of the transistor and a ground, a first feedback capacitor connected between a base and an emitter of the transistor, a second feedback capacitor connected between the emitter of the transistor and the ground, and an emitter follower connected to the emitter of the transistor. In a package, a stray reactance and a bonding wire are designed so as to agree with an element value and a Q value which can be used as parts of a resonator. A surface elastic wave resonator disposed outside the integrated circuit is connected between the base of the transistor and the ground. The oscillator is voltage controlled by a variable capacitance diode connected in series with the resonator.