A semiconductor optical device includes: a ridge stripe structure portion 20 in which a first compound semiconductor layer 31, an active layer 32, and a second compound semiconductor layer 32 are stacked and which has a first end surface 21 which emits light and a second end surface 22 opposite to the first end surface 21; and a current regulation region 41 provided to be adjacent to at least one of ridge stripe adjacent portions 40 positioned at both sides of the ridge stripe structure portion 20, at the second end surface side, and to be away from the ridge stripe structure portion 20. A bottom surface of the current regulation region 41 is under the active layer 33, and a top surface of the ridge stripe adjacent portion 40 excluding the current regulation region 41 is above the active layer 33.