A superluminescent diode includes a substrate; a double heterojunction structure including a first conductivity type cladding layer, an undoped or first or second conductivity type active layer, and a second conductivity type cladding layer disposed on said substrate; a first conductivity type cap layer disposed on the second conductivity type cladding layer; and a second conductivity type stripe-shaped diffusion region penetrating the cap layer and reaching into the second conductivity type cladding layer. Current is injected into the active layer through the diffusion region. The stripe-shaped diffusion region extends from a front facet toward but not reaching a rear facet and is inclined an angle in a range from 3 to 20 degrees with respect to the front facet. Accordingly, repetition of reflection and amplification of light having a directionality perpendicular to the facets is decreased and the effective reflection of light from both facets is decreased, resulting in an SLD that can operate stably even in high power output operation without inviting laser oscillation and that can be produced with a high yield.