To provide a fluid sterilizer capable of increasing the efficiency of irradiating a fluid with ultraviolet light to improve the efficiency of sterilizing the fluid.SOLUTION: A fluid sterilizer 1 includes: a cylindrical flow path portion 2 having an inner diameter of 24 mm or more and 64 mm or less and forming a fluid flow path 21； a reflection portion 22 provided on the outer surface of the flow path portion 2； a window portion 23 formed in the longitudinal direction of the flow path portion 2 and not provided with the reflection portion 22； and a light source portion 4 in which a plurality of light emitting elements 41 for radiating ultraviolet light are disposed along the window portion 23.SELECTED DRAWING: Figure 1【課題】流体への紫外光の照射効率を高め、流体の殺菌効率を向上す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、内径が２４ｍｍ以上６４ｍｍ以下であって、流体の流路２１を形成する筒状の流路部２と、前記流路部２の外面に設けられた反射部２２と、前記流路部２の長手方向に形成され、前記反射部２２が設けられていない窓部２３と、紫外光を照射する複数の発光素子４１が前記窓部２３に沿って配設された光源部４とを具備する。【選択図】図１
