A light source device includes: a tubelar body disposed in the front side of a reflection mirror in the light emission direction and surrounding an arc tube; a pair of ducts connecting with the tubelar body and provided with a first channel and a second channel to guide air; and a channel switching mechanism which allows air to flow through the first channel or the second channel. The tubelar body includes a pair of communicating ports configured to supply air flowing through the first channel and the second channel toward the light emission portion. The pair of the communicating ports are disposed on a virtual line passing through the center line of the arc tube and crossing the vertical direction and the horizontal direction as viewed in a direction along the center line.