A semiconductor optical device includes: a group III nitride semiconductor substrate having a primary surface of a first orientation; a first group III nitride semiconductor laminate including a first active layer disposed on a first region of the primary surface; a group III nitride semiconductor thin film having a surface, which has a second orientation different from the first orientation, disposed on a second region, the second region being different from the first region; a junction layer provided between the second region and the group III nitride semiconductor thin film; and a second group III nitride semiconductor laminate including a second active layer and disposed on the surface of the group III nitride semiconductor thin film. The first and second active layers include first and second well layers containing In, respectively, and the emission wavelengths of the first and second well layers are different from each other.