PROBLEM TO BE SOLVED: To provide an ultraviolet irradiation device which efficiently irradiates ultraviolet rays and has high durability. SOLUTION: A fluid sterilization module 1 provided with an ultraviolet irradiation device has an inner cylinder 21, a case portion 22 accommodating the inner cylinder 21, and an outer peripheral surface of the inner cylinder 21 and an inner peripheral surface of the case portion 22. The first chamber 26 and the member 24, which are regions on one end side of the inner cylinder 21 with respect to the member 24, in the tubular gap between the member 24 provided in close contact with the inner cylinder 21 and the case portion 22. The second chamber 27, which is the region on the other end side of the inner cylinder 21, the inflow portion 4 in which the object flows into the first chamber 26, and the outflow portion 5 in which the object flows out from the second chamber 27. A light emitting element 34a provided on at least one of one end side or the other end side of the cylinder 21 and irradiating ultraviolet light toward an object passing through the processing flow path 21d, and the object being in the processing flow path 21d. A fluid detector 6 for detecting 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. [Selection diagram] Figure 2【課題】効率よく紫外線照射を行い且つ耐久性の高い紫外線照射装置を提供する。【解決手段】紫外線照射装置を備えた流体殺菌モジュール１は、内筒２１と、内筒２１を収容するケース部２２と、内筒２１の外周面とケース部２２の内周面との間に密着して設けられた部材２４と、内筒２１とケース部２２との間の筒状の隙間のうちの、部材２４よりも内筒２１の一端側の領域である第一室２６及び部材２４よりも内筒２１の他端側の領域である第二室２７と、第一室２６に対象物を流入する流入部４と、第二室２７から対象物を流出させる流出部５と、内筒２１の一端側又は他端側の少なくとも一方に設けられ、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、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。【選択図】図２
