The present invention pertains to an ultraviolet sterilization device comprising: a transfer pipe (2) having an inlet port (4) and an outlet port (5); and an ultraviolet light source (3) that causes ultraviolet rays to be incident to the transfer pipe. Fluid to be treated that is inside the transfer pipe is sterilized by the ultraviolet rays irradiated from the ultraviolet light source. At least the inner peripheral surface of the transfer pipe is formed from a material having a smaller refractive index than the refractive index of the fluid to be treated that flows through the transfer pipe. The ultraviolet rays irradiated on the fluid to be treated are irradiated so as to be completely reflected by the inner peripheral surface of the transfer pipe.