In one embodiment, a light source device comprises a container with a duct unit disposed above an arc tube and extends along the center axis of light reflected by a reflection surface such that cooling air can flow in a direction opposite to the traveling direction of light reflected by the reflection surface. The duct unit includes a first opening disposed at a position shifted toward the traveling direction side from an opening end of the first reflection mirror, a wall portion which forms the edge of the first opening on the side opposite to the traveling direction side as a final end of the duct unit, and an inclined portion disposed in the vicinity of the edge of the first opening on the traveling direction side to bend the flowing direction of the cooling air toward an upper surface opposite to the surface having the first opening.