A semiconductor optical element includes a first cladding layer; a second cladding layer formed in a ridge shape; and optical confinement layer interposed between the first cladding layer and the second cladding layer to propagate light, wherein the second cladding layer is configured with a ridge bottom layer; a ridge intermediate layer; and a ridge top layer in this order from the optical confinement layer, and the ridge intermediate layer is formed wider in cross section perpendicular to the optical axis—the light propagating direction in optical confinement layer—than the ridge bottom layer and the ridge top layer.