Abstract: A wavelength-tunable laser device includes: a wavelength-tunable light source part; an optical filter; a light receiving element; and a control device. Further, the control device includes: a monitor value calculating part configured to calculate a monitor value; a storage part configured to store wavelength control information; a target value calculating part configured to calculate a control target value; and a wavelength control part configured to control the wavelength of the laser beam to be the target wavelength, and the wavelength control information is information in which a wavelength, a control reference value, and mode identification information are associated with each other, and the target value calculating part calculates the control target value based on the wavelength control information stored in association with the same mode identification information when the same wavelength as the target wavelength is different from the wavelength control information stored in the storage part.