An oscillator having a negative resistance device and a resonator includes: a transmission line connected to the negative resistance device; a three-terminal device including a first terminal connected to the signal line side of the transmission line at a terminal part, a second terminal connected to the grounding line side of the transmission line and a third terminal receiving a control signal applied thereto; a first regulation unit for regulating the control signal to be applied to the third terminal; and a second regulation unit for regulating the voltage to be applied to the second terminal, the first and the second regulation unit being adapted to regulate respectively the control signal and the voltage so as to make the characteristic impedance of the transmission line and the impedance between the first and the second terminal show an impedance matching. The power consumption rate of the stabilizing circuit can be reduced.