A range finding device having a light projector and a light receiver. The light projector has a mirror for reflecting toward a subject near-infrared light emitted laterally from an IRED. The mirror has a reflection surface extending farther in a direction perpendicular to the base line direction than in the base line direction. According to the embodiment of this invention, for a light source unit, a base plate holding a plurality of IREDs is packaged in a transparent plastic package. The base plate is formed with arms extending out of the package. The light source unit is fixed on the camera body by the arms. The light receiver also uses a base plate with the similar arms.