A light-emitting unit for superimposement is provided. The light-emitting unit is applied to one of a pentagonal roof-mirror or a pentagonal Dach-prism of a viewfinder optical system of a camera. The unit comprises a light source, a light-emitting lens, and a second mirror. The light source emits superimposing light. The second mirror reflects light emitted from the light source and passed through the light-emitting lens toward a third reflection face of one of a pentagonal roof-mirror or a pentagonal Dach-prism. The light source, the light-emitting lens, and the second mirror are integrally assembled as a unit.