A method for controlling a wavelength tunable laser is disclosed. The method comprises the steps of: calculating a lasing wavelength from two or more kinds of parameters, the parameters designating the target lasing wavelength; acquiring a driving condition from a memory, the wavelength tunable laser being operable to generate a laser beam of a first wavelength in the driving condition; and calculating another driving condition from the driving condition thus acquired and a wavelength difference between the first wavelength and a second wavelength, the second wavelength corresponding to the lasing wavelength, the wavelength tunable laser being operable to generate a laser beam of the second wavelength in the another driving condition, the wavelength tunable laser being driven in the another driving condition.