A light source device includes a light emitting tube having a light emitting section that emits light, a first sealing section on one side of the light emitting section formed integrally with the light emitting section, and a second sealing section on the other side of the light emitting section formed integrally with the light emitting section. A secondary reflecting mirror having a secondary reflecting surface covers part of a periphery of the light emitting section and reflects light emitted from the light emitting section. A primary reflecting mirror having a primary reflecting surface reflects the light emitted from the light emitting section and the light reflected by the secondary reflecting mirror. The secondary reflecting mirror has a first reference plane defined by a first boundary line as a boundary between the light emitting section and the first sealing section, which does not intersect with the secondary reflecting surface.