A light source device includes an outer housing, a partitioning member for forming a multi-stage structure in the outer housing, thereby partitioning each stage, a plurality of light source units disposed in respective stages of the outer housing, each of which has light source members and a heat pump unit for cooling the light source members, an opening portion for taking air acting as cooling air to be supplied to a cooling body from an outer part of the outer housing into an inner part thereof, and an opening portion formed along arrangement of the light source units in the partitioning member.