A semiconductor light emitting device capable of correcting astigmatism difference well and oscillating stably also at the time of a high output operation, wherein a waveguide stripe width at the center of a stripe portion is constant, an inter-ridge recessed portion width (ridge separation width) is set narrow at the center portion of the stripe portion (resonator center portion), and a ridge separation width near an end surface side is set broader than the ridge separation width at the center portion, whereby a waveguide mode of the stripe center portion is laterally spread and in addition the current can be held in the narrow region and, accordingly, a saturable absorbing region is formed in the lateral region inside an active layer, pulsation can be stably induced, and an effective refractive index difference An near the end surface is made large and an index guide-like waveguide can be obtained, whereby astigmatism difference can be reduced to close to zero.