PURPOSE: To provide the high frequency oscillator which very reduces the area of stub formation for frequency adjustment to extend the frequency adjustment width and is capable of coarse and fine adjustment of the frequency.

CONSTITUTION: This high frequency oscillator consists of a resonance circuit part provided with a micro strip line 1, which has one end grounded, and a negative resistance circuit part, and the micro strip line 1 is provided with a first adjusting means which adjusts the line width to vary the oscillation frequency, for example, plural disconnectable conductor branch lines 11 to 13 and a second adjusting means which adjusts the line length to vary the oscillation frequency, for example, disconnectable short stubs 21 to 25 in parallel.