The present invention is characterized by comprising: forming a stacked structure in which a lower cladding layer, an active layer and an upper cladding layer are stacked on an InP substrate in a shape having a mesa stripe structure; forming a first insulation film on the stacked structure by a sputtering method; forming a second insulation film thinner than the first insulation film, on the first insulation film by a plasma CVD method at a film forming temperature higher than that when the first insulation film has been formed; and forming a first electrode on the upper cladding layer, and forming a second electrode on a back surface of the InP substrate.