To provide a light source device capable of restraining the occurrence of irradiation nonuniformity, while providing high illuminance for a light irradiation object area positioned in the central part of a light irradiation surface.

This light source device has a reflecting mirror having an opening in front and a halogen electric lamp arranged so that a filament coil is positioned on the optical axis of the reflecting mirror, and is characterized in that the reflecting mirror has a reflecting surface constituted by continuously arranging a plurality of convex facets for reflecting the light emitted from the halogen electric lamp, and the convex facets have a shape of 1.2 to 10 in the ratio (R1/R2) of a radius of curvature R1 in the extending direction of the optical axis of the reflecting mirror projected on a convex curved surface to a radius of curvature R2 in the orthogonal direction to the optical axis projected on the convex surface.