A light source unit includes a plurality of LED elements; an LED substrate that comprises a plurality of subdivided regions arrayed in a circumferential direction at least at an outwardmost locus as viewed from a direction perpendicular to the mounting surface; and cooling member(s) which are provided at surface(s) on a side opposite the mounting surface of the LED substrate and at which provided at each of the plurality of subdivided regions there are inlet port(s) for flow thereinto of cooling medium for cooling LED element(s), outlet port(s) that are for discharge of cooling medium and that are disposed more toward a center of the LED substrate than inlet port(s) as viewed from the direction perpendicular to the mounting surface of the LED substrate, and flow passage(s) which connect inlet port(s) and outlet port(s) and through interior(s) of which cooling medium flows.