An endoscope light source device includes: a plurality of solid-state light sources； a plurality of collimating lenses that respectively collimate light beams emitted from the plurality of solid-state light sources into substantially parallel light beams； a multiplexing optical member that multiplexes the light beams that have been collimated into substantially parallel light beams by the plurality of collimating lenses； at least one diaphragm disposed between at least one of the plurality of solid-state light sources and a corresponding at least one of the plurality of collimating lenses； and a focusing lens that focuses multiplexed light beams from the plurality of solid-state light sources and causes the light beams to enter an end surface of a light guide of an endoscope, wherein the at least one diaphragm blocks more peripheral light as an optical path length from each of the plurality of solid-state light sources to the focusing lens becomes smaller.
