To provide a fluid sterilization device that can prevent condensation on a window member.SOLUTION: A fluid sterilization device 10 comprises: a treatment channel 12 through which fluid to be sterilized flows； a light source 14 that irradiates ultraviolet light toward the fluid in the treatment channel 12； a window member 16 provided between the light source 14 and the treatment channel 12 and having an incidence surface 17 on which the ultraviolet light from the light source 14 is incident and an output surface 18 through which the ultraviolet light is output toward an inside of the treatment channel 12； and a heating member 40 provided so as to be brought into contact with a part of the incident surface 17 and for heating the window member 16.SELECTED DRAWING: Figure 1【課題】窓部材の結露を防止できる流体殺菌装置を提供する。【解決手段】流体殺菌装置１０は、殺菌対象の流体が流れる処理流路１２と、処理流路１２内の流体に向けて紫外光を照射する光源１４と、光源１４と処理流路１２の間に設けられ、光源１４からの紫外光が入射する入射面１７と、処理流路１２内に向けて紫外光が出射する出射面１８とを有する窓部材１６と、入射面１７の一部と接触するように設けられ、窓部材１６を加熱する加熱体４０と、を備える。【選択図】図１
