A method of controlling a wavelength-tunable laser selecting an oscillation wavelength with a combination of a plurality of wavelength selection portions of which wavelength peak is different from each other, comprising: a first step of confirming a control direction of the wavelength selection portion in a case where a setting value is changed from a first setting value for achieving the first wavelength to a second setting value for achieving the second wavelength; a second step of setting a setting value that is shifted from the second setting value in a direction that is opposite of a pre-determined changing direction on the wavelength selection portion as a prepared setting value, when the control direction confirmed in the first step is opposite to the pre-determined changing direction; and a third step of changing the prepared setting value set in the second step to the second setting value.