A semiconductor optical device includes a laminated structure constituted of a first compound semiconductor layer of an n type, an active layer, and a second compound semiconductor layer of a p type, the active layer including at least 3 barrier layers and well layers interposed among the barrier layers, and the semiconductor optical device satisfying Egp-BR>Egn-BR>EgWell when a bandgap energy of the barrier layer adjacent to the second compound semiconductor layer is represented by Egp-BR, a bandgap energy of the barrier layer between the well layers is represented by EgWell, and a bandgap energy of the barrier layer adjacent to the first compound semiconductor layer is represented by Egn-BR.