A light source device includes: a light source lamp; and a housing, wherein the housing includes: a pair of openings formed, along a top and bottom with direction of a luminous flux emission of the light source device; a duct member provided so as to cover the pair of openings, and having an intake which outside air is introduced from the pair of openings to an air flow channel upstream side; a first air flow guide member provided inside the duct member, and causing the air introduced from the intake to circulate to either one of the pair of openings via the duct member by pivots under its own weight; and a second air flow guide members provided in positions in the housing corresponding to the openings, and causing the air introduced from the openings to circulate toward the light source lamp.