A light source device according to the present disclosure is provided with a light emitting element, a light guide member, a support member for supporting the light guide member in a groove part, and a holding member for holding the light guide member outside the groove part. The first face of the light guide member emits light guided by the light guide member, the light emitting element is disposed so as to be opposed to the third face, and the groove part has a support surface, a first wall surface, and a second wall surface. The light guide member has a protruding part which protrudes outside the groove part in at least one of both end portions on the first axis, and the protruding part is held by the holding member.