An optical transmitter includes: a semiconductor laser unit that outputs laser light of first output power and outputs a monitor current; a casing of an optical module that holds optical fiber; a monitor current detection unit that generates a monitor voltage; a laser driving unit that controls a laser driving current; a storage unit that stores information based on a result of a measurement of a ratio of second output power with respect to the first output power; a target voltage determination unit that changes the target voltage based on a detected temperature of a temperature sensor and the information based on the result of the measurement; and a power monitor value determination unit that generates a power monitor value indicating the second output power to be transmitted to a host device using the detected temperature and the information based on the result of the measurement.