PROBLEM TO BE SOLVED: To provide an ultraviolet irradiation device which sterilizes more reliably and efficiently irradiates ultraviolet rays. SOLUTION: A fluid sterilization module 1 communicates with an inner cylinder 21 forming a tubular processing flow path 21d extending in the longitudinal direction and a processing flow path 21d through an opening on one end side of the inner cylinder 21. In addition to the chamber 26, the inflow portion 4 that allows the object to flow into the first chamber 26, the outflow portion 5 that allows the object that has passed through the treatment flow path 21d to flow out from the other end side of the inner cylinder 21, and the treatment flow path 21d. A light emitting element 34a that is provided facing the opening on the end side and irradiates ultraviolet light along the longitudinal direction toward the object passing through the processing flow path 21d, and the object is in the processing flow path 21d. A fluid detector 6 for detecting the above, and a control unit 7 for driving and controlling the light emitting element 34a based on the detection signal of the fluid detector 6 are provided. The internal volume of the first chamber 26 is 2/3 or more of the cube of the equivalent inner diameter of the processing flow path 21d and 3 times or less the internal volume of the processing flow path 21d. [Selection diagram] Figure 2【課題】より確実に殺菌を行い、効率よく紫外線照射を行う紫外線照射装置を提供する。【解決手段】流体殺菌モジュール１は、長手方向に延びる筒状の処理流路２１ｄを形成する内筒２１と、内筒２１の一端側の開口部を介して処理流路２１ｄと連通する第一室２６と、第一室２６に対象物を流入する流入部４と、処理流路２１ｄを通過した対象物を内筒２１の他端側から流出させる流出部５と、処理流路２１ｄの他端側の開口部に面して設けられ、処理流路２１ｄを通過する対象物に向けて長手方向に沿って紫外光を照射する発光素子３４ａと、対象物が処理流路２１ｄ内にあることを検知する流体検知器６と、流体検知器６の検知信号に基づき発光素子３４ａを駆動制御する制御部７と、を備える。第一室２６の内容積は、処理流路２１ｄの相当内径の三乗の２／３以上、処理流路２１ｄの内容積の３倍以下である。【選択図】図２
