To provide a light source device ensuring a high utilization rate of light, for ultraviolet light of low wavelength radiated from a short arc flash lamp.

A short arc flash lamp comprises: a luminous tube provided, at both ends of a substantially spherical light-emitting section, with sealing portions elongating outward in the tube axis direction; a pair of discharge electrodes arranged in the light-emitting section to face each other in the tube axis direction; and a trigger electrode disposed so that the tip is located between the discharge electrodes. The light-emitting section is filled with an inert gas of 1×10⁵ Pa or higher. The short arc flash lamp is further provided with a concave reflector disposed to surround the light-emitting section, and having a rotary elliptic or rotary parabolic light reflection surface. The light-emitting section is composed of a material having a refractive index of 1.55 or less for the light having a wavelength of 200 nm, and satisfies a relation 1/3≤b/a≤3, where a is the radius in the tube axis direction, and b is a radius in the direction perpendicular to the tube axis direction.