A light source device includes: an arc tube having a bulb portion and a sealing portion; a reflector which fixes the arc tube; and a holding portion which holds the reflector, wherein the holding portion includes an inlet port, a partition provided between the inlet port and the arc tube, a pair of passages to which diverges in the partition and can circulate the cooling air to the arc tube, a first opening provided in the partition, and a shutter which is provided on that side of the partition where the inlet port is located, rotates about a rotation axis, and blocks a lower passage of the pair of passages, and on that side of the shutter where the rotation axis is located, a second opening is provided so as to overlap the first opening as seen from the inlet port.