A light emitting device includes: a single crystal substrate having a plane tilted from a low-index plane and first and second cladding layers sandwiching an active layer, wherein the active layer includes first and second parallel side surfaces, part of the active layer constitutes first and second gain regions, a first side surface reflectance is higher than a second side surface reflectance, each of the first and second gain regions is disposed from a first side surface end surface to a second side surface end surface, the first gain region end surface partially overlaps the second gain region end surface so the end surfaces do not overlap each other in the first and second gain regions, a perpendicular of the first side surface is parallel to an off-direction of the substrate, and the first and second gain regions have equal lengths.