A superluminescent diode which amplifies light through stimulated amplification and outputs emitted beams from one of edges at two ends includes a cladding layer of a first conductivity type formed on a semiconductor substrate, an active layer formed on the cladding layer of the first conductivity type, a cladding layer of a second conductivity type formed on the active layer, and a multilayer film formed at the other edge opposite to the one edge that emits the beams, reflectance of which has wavelength dependence, and a spectral shape of the emitted beams output from the one edge is controllable by the multilayer film.