The light source device includes: a first support that supports one of a light source and a collimator lens condensing; a second support that supports the other of the light source and the collimator lens; and a fixing member that fixes the first support to the second support. The first support includes a first protruding portion that protrudes from the first support toward the second support, the first protruding portion having a through hole therethrough. The second support includes a second protruding portion that protrudes from the second support toward the first support, the second protruding portion having: a receiving portion that receives the first protruding portion; and a receiving hole. A rod portion of a locking member is inserted into the through hole and the receiving hole, and a head portion of a locking member is sealed with a sealant.