Fluid sterilization device

A fluid sterilization device comprising:

• a processing flow passage in which a fluid subject to sterilization flows;
• a window member provided between a light source for irradiating the fluid in the processing flow passage with ultraviolet light and the processing flow passage, the window member including an incidence surface on which the ultraviolet light from the light source is incident and an exit surface from which the ultraviolet light exits toward the processing flow passage;
• and
• a thermally conductive heating body comprising a contact part and a connection part, wherein the heating body is adapted to heat the window member by transferring heat generated by the light source to the window member through the contact part and the connection part, wherein the contact part that is in contact with the incidence surface and the connection part extends from the light source to the contact part wherein the contact part is provided to be in contact with the incidence surface both in a central region of the incidence surface and in an outer circumferential region of the incidence surface outside the central region.