To downsize a light source unit without degrading efficiency in using light from a light source.

The light source unit 2 includes: a lamp 4 that emits radiation light; an annular lens 6 disposed on an optical axis K; and a reflector 5 by which part of the light emitted from the lamp 4 is reflected and made incident on the annular lens 6. The annular lens 6 refracts at least part of the light reflected by the reflector 5, and makes it incident on the incident face of a light guide rod 3.