To provide an ultraviolet irradiation device that can reduce the decrease in the sterilization effect due to the provision of a rectification chamber.SOLUTION: The fluid sterilization module 1 including an ultraviolet irradiation device comprises: an inner cylinder 21 forming a cylindrical processing flow path 21d extending in the longitudinal direction； a first rectifying chamber 26 provided along the outer peripheral surface on one end side of the inner cylinder 21 and communicating with the processing flow path 21d through the opening on the one end side of the inner cylinder 21； an inflow part 4 for flowing an object into the first rectifying chamber 26； an outflow part 5 for flowing out the object that has passed through the processing flow path 21d from the other end side of the inner cylinder 21； and a light-emitting element 34a for irradiating ultraviolet light toward the object passing through the processing flow path 21d, and in which, in a cross section orthogonal to the longitudinal direction at a position including the first chamber 26 of the inner cylinder 21, the cross-sectional area of the first chamber 26 is 1/10 or more and 1 or less of the cross-sectional area of the processing flow path 21d.SELECTED DRAWING: Figure 2【課題】整流室を設けることによる殺菌効果の低下を、より小さくすることの可能な紫外線照射装置を提供する。【解決手段】紫外線照射装置を有する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の一端側の外周面に沿って設けられ内筒２１の前記一端側の開口部を介して処理流路２１ｄと連通する整流用の第一室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を通過する対象物に向けて紫外光を照射する発光素子３４ａと、を備え、内筒２１の第一室２６を含む位置における、長手方向と直交する断面において、第一室２６の断面積が処理流路２１ｄの断面積の１／１０以上１以下である。【選択図】図２
