A laser module has two semiconductor laser devices and a laser driving circuit. These laser devices are placed adjacent to each other. The laser driving circuit has normal and reverse phase data output terminals. One semiconductor laser device is connected to the normal phase data output terminal, and the other semiconductor laser device is connected to the reverse phase data output terminal. When a series of identical bits is output, the temperature changes of the two laser devices are complementary. Accordingly, the temperature variation of each laser device is moderated. Thus, the variation in the amount of chirp can be reduced.