To realize a light source unit which is capable of low-noise lamp cooling without blowing hot air out.

A lamp base 13 where a reflector 12 reflecting the light from a lamp bulb 11 as a heat generation source and a lamp bulb 11 are fixed with an adhesive 14 is joined with a heat transport flat plate 15 which forms a plane type heat radiator wherein a zigzag thin pipe containing a refrigerant is incorporated, and the heat transport flat plate 15 is brought into close contact with the internal wall surface of a housing 17 to radiate the heat of the lamp bulb 11 to outside and inside the housing by natural convection through the heat conduction path of the lamp base 13 and heat transport flat plate 15. The lamp base 13 made of ceramic etc., of ≥17W/(mK) in heat conductivity is extended until the lamp base abuts against or is closed to the bulb part of the lamp bulb 11 to efficiently conduct the heat generated by a high-luminance lamp bulb 11 of 150W. Further, a metal material 16, a cushion material 16b, etc., are provided at the arbitrary place of the lamp base 13 and the joined surface of the heat transport flat plate 15.