A light source apparatus comprising a lamp having a light emitting portion of generating light, a first concave mirror having a first opening provided on a light-using side on which the generated light is used and a second opening provided on an opposite side to the light-using side and having the light emitting portion of the lamp placed inside, and a second concave mirror having a predetermined size to reflect on the light emitting portion side of the lamp the light which comes or should come out of the second opening and placed at a predetermined position in relation to a position at which the second opening is provided, and wherein the size of the second opening is provided so that an amount of the used light becomes substantially maximum.