A light source device according to an embodiment of the present disclosure includes: a light source section; a rotating body; a motor; a housing; one or more lens groups; a lens holding section; and an adjusting mechanism. The rotating body includes a fluorescent light body. The fluorescent light body is excited by excitation light from the light source section to output fluorescent light. The motor drives the rotating body. The housing accommodates the rotating body. The one or more lens groups gather the excitation light from the light source section and direct the excitation light toward the rotating body. The lens holding section holds the one or more lens groups. The adjusting mechanism adjusts a distance between the rotating body and the one or more lens groups.