Provided is a power saving and highly reliable wavelength tunable laser device.A wavelength tunable laser device 10 of the present invention includes: a wavelength tunable laser 11 including: a laser resonator including a light source 111 and wavelength tunable mechanisms 112 and 113; and light loss control units 114a and 114b; a temperature detecting element 12 detecting a temperature of the wavelength tunable laser 11; and a controller 13, wherein the controller 13 obtains temperature information a of the wavelength tunable laser 11 from the temperature detecting element 12, calculates wavelength tunable control parameters d and e and light loss control parameters b1 and b2 based on the temperature information a, controls the wavelength tunable mechanisms 112 and 113 based on the wavelength tunable control parameters d and e, and controls light loss control units 114a and 114b based on the light loss control parameters b1 and b2.