An optical transmitter includes: a wavelength tunable light source; an etalon filter that filters output light of the light source; a measurement unit that generates a monitor value corresponding to power of output light of the etalon filter; and a controller that controls a temperature of the light source and a temperature of the etalon filter. Until the wavelength of the output light of the light source is adjusted to a target wavelength, the controller alternately performs first processing to control the temperature of the light source based on the monitor value so as to shift the wavelength of the output light of the light source by a specified amount, and second processing to control the temperature of the etalon filter based on the monitor value so as to shift the transmission characteristics of the etalon filter by the specified amount.