A tunable laser has a multiple ring resonator comprising a plurality of ring resonators having respective ring-shaped waveguides and respective different optical path lengths, an input/output side optical waveguide coupled to the multiple ring resonator, an optical input/output device such as a laser diode coupled to the input/output side optical waveguide, a reflection side optical waveguide coupled to the multiple ring resonator, an optical reflector coupled to the reflection side optical waveguide for removing light at an unwanted wavelength and reflecting light at a required wavelength, and a wavelength varying mechanism for changing the resonant wavelength of the multiple ring resonator.