To provide a distribution constant line type oscillator which improves a load Q in comparison with conventional one, is stabilized in frequency manner and reduces phase noises.

To the gate of a field effect transistor(FET) Tr as an oscillation element, an n/2 {(n) is a natural number ≥2} wavelength resonators Res composed of distribution constant lines is connected. Since the reactance of the resonator Re is made n-fold in comparison with the case of using a 1/2 wavelength resonator, the load Q=Q1 of the oscillator is improved. The generation of unwanted oscillation caused by extending the electric length of the resonator Res can be prevented by providing parallel resonance circuits L and C on the source side of the FET Tr and limiting a frequency band for the appearance of negative resistance at the gate by setting its anti-resonance frequency a little lower than the desired oscillation frequency. Drain parallel resonance circuits having the anti-resonance frequency a little higher than the desired oscillation frequency can be provided as well. A voltage controlled reactance element can be provided at one end of the resonator Res as well. A (n/2+1/4) wavelength resonator can be used as well.