A wavelength tunable light source includes a wavelength tunable laser device and a control device. The wavelength tunable laser device includes: M laser diodes configured to generate laser oscillation to output beams; a multiplexer/demultiplexer configured to multiplex the beams output from the M laser diodes to bifurcate the beams for output; a first semiconductor optical amplifier configured to amplify one output beam of the bifurcated beams to output a first emitted beam; and a second semiconductor optical amplifier configured to amplify another output beam of the bifurcated beams to output a second emitted beam. The control device is configured to perform wavelength switching control on wavelengths of the first emitted beam and the second emitted beam by switching an electric power input to the second semiconductor optical amplifier.