An active layer of a semiconductor laser element held by a laser mount is formed to be closer to the bottom than to the center of the height of the semiconductor laser element. A laser beam emitted from the active layer passes through a collective lens and an optical isolator and enters an incidence portion of an optical fiber. Returning light reflected by the incidence portion of the optical fiber passes through the optical isolator and the collective lens and is collected onto an end face of the laser mount. The optical isolator includes first and second rutiles which transmit normal light with refraction and abnormal light without refraction, a Faraday element which rotates a polarization plane of transmitted light in the clockwise direction by 45 degrees, and a permanent magnet for applying a magnetic field to the Faraday element.