To provide a fluid sterilizer capable of increasing sterilization efficiency by uniformizing velocity distribution of a fluid to reduce variations in irradiation time of ultraviolet light.SOLUTION: The fluid sterilizer 1 comprises a cylindrical body 5 having a flow path through which a fluid to be sterilized flows, an inflow port 6a provided on one end side of the cylindrical body 5, an outflow port 7a provided on the other end side of the cylindrical body 5, a light source 3 for irradiating the fluid with ultraviolet light, and a flow straightening plate 12 provided in the flow path and having a cylindrical through hole. The flow straightening plate 12 consists of an inner peripheral region Rextending from its center in the radial direction of the flow path, and an outer peripheral region Rextending outside the inner peripheral region R, wherein the ratio of the plate thickness t to the diameter d of the through hole in the outer peripheral region R, (t/d)is larger than the ratio of the plate thickness t to the diameter d of the through hole in the inner peripheral region R, (t/d).SELECTED DRAWING: Figure 2【課題】流体の速度分布を均一化して紫外光の照射時間のばらつきを低減し、殺菌効率を高めることができる流体殺菌装置を提供する。【解決手段】流体殺菌装置１は、殺菌対象の流体が流れる流路を有する筒体５と、筒体５の一端側に設けられた流入口６ａと、筒体５の他端側に設けられた流出口７ａと、流体に紫外光を照射する光源３と、流路内に設けられ、円柱状の貫通孔を有する整流板１２を備えている。整流板１２は、その中心から流路の径方向に延在する内周領域Ｒinと、内周領域Ｒinの外側に延在する外周領域Ｒoutとからなり、外周領域Ｒoutにおける板厚ｔの貫通孔の直径ｄに対する比（ｔ／ｄ）outは、内周領域Ｒinにおける板厚ｔの貫通孔の直径ｄに対する比（ｔ／ｄ）inよりも大きい。【選択図】図２
