A photoelectric oscillator includes a laser beam projection unit; an optical modulator on an optical path extending from the projection unit, which optical modulator outputs a modulated signal or an optical signal containing a harmonic of the modulated signal and includes a modulation electrode whose resonant frequency band includes the frequency band of the modulation signal; a photoelectric converter for converting the output of the optical modulator to an electric signal; a feedback circuit for selecting from the radio-frequency electric signal obtained from the photoelectric converter an electric signal to be re-supplied to the optical modulator; and an output section for outputting an optical signal containing the modulation signal or a harmonic of the modulation signal or outputting the modulation signal or a harmonic of the modulation signal. A laser beam of sufficient intensity is input from the projection unit to produce a radio-frequency electric signal in the feedback circuit, and the radio-frequency electric signal or an optical signal containing the radio-frequency electric signal or the radio-frequency signal is output from the photoelectric oscillator.