PURPOSE: To oscillate a semiconductor laser stably at a single wavelength, in a distributed feedback type semiconductor laser, by forming one end surface at a position, which is separated from the top of the protruded part or the lowest point of the recess part in a periodic wave form by 1/6∼1/10 the wave period.

CONSTITUTION: The left end surface of a semiconductor laser is controlled and formed at a position, which is separated from a top 17 of the protruded part of a periodic wave form by Λ/8. (In this case, Λ is the length of the wave period. It is determined as 2,400 in this embodiment. Therefore, Λ/8 becomes about 300.) In order to enhance the reflectivity at the end surface, a reflecting film 16 is formed. The left end part of the distributed feedback type semiconductor laser undergoes the phase shift of Λ/4. The reflectivity at this point is enhanced by the reflecting film 16. Therefore, the same wave conducting mode as that of a distributed feedback type semiconductor laser having the phase shift of Λ/4 at the central part is obtained. Therefore, A TE-1 mode and a TE+1 mode have the same frequency. Thus the stable oscillation can be obtained at a single wavelength.