An n-Inp buffer layer, a GRIN-SCH-MQW active layer, and a p-InP spacer layer are laminated on an n-InP substrate. A p-InP blocking layer and an n-InP blocking layer are provided to be adjacent to an upper region of the n-InP buffer layer, the GRIN-SCH-MQW active layer and the p-InP spacer layer. A p-InP cladding layer, a p-GaInAsP contact layer, and a p-side electrode are laminated on the p-InP spacer layer and the n-InP blocking layer, and an n-side electrode is arranged on a rear surface of the n-InP substrate. A diffraction grating that selects light having the number of oscillation longitudinal modes of not less than 10, more preferably not less than 18, oscillation longitudinal modes the difference values of which in optical intensity from the oscillation longitudinal mode having the highest optical intensity are not more than 10 dB, is arranged in the p-InP spacer layer.