A wavelength stabilized source of light has a laser diode (101) which emits a laser beam having a wavelength of 1.56 mu m. Double harmonic generating means (105) generates double harmonic light of the laser beam. The double harmonic light enters to a resonator (102) having <87>Rb atoms. The resonator (102) is irradiated with microwaves whose phase is modulated. The resonator (102) forms double resonance signals when the wavelength of the double harmonic light is equal to the resonance wavelength of <87>Rb and when the frequency of the microwaves is equal to the transition frequency of <87>Rb. A first control circuit (103) so controls the microwaves that the frequency of the microwaves will become equal to the transition frequency. A second control circuit (104) so controls the laser diode (101) that the wavelength of the double harmonic light will become equal to the resonance wavelength of <87>Rb. Therefore, the laser beam that is generated has a stable wavelength of 1.56 mu m.
