An irradiation apparatus 10 is provided with: a straight pipe 20 that is formed of polytetrafluoroethylene (PTFE)； and a light source 40 that is arranged at an end portion (first end portion 22) of the straight pipe 20 and that irradiates the inside of the straight pipe 20 with ultraviolet light. The light source 40 has a light emitting device 42 that emits ultraviolet light and an adjustment mechanism 50 that adjusts the direction of the ultraviolet light such that the ultraviolet light from the light emitting device 42 becomes incident on the internal wall surface 20a of the straight pipe 20 at an incident angle ¸ of 75 degrees or more.
