PROBLEM TO BE SOLVED: To facilitate replacement of parts while suppressing a temperature rise of a light source. The fluid sterilizer of the embodiment includes a processing unit, a light source unit, a cover member, and a flow path member. The processing unit processes the fluid. The light source unit includes a light source that irradiates an ultraviolet ray toward the processing unit and a support member that supports the light source. The cover member is arranged on the front side of the light source portion to protect the light source from the fluid. The flow path portion has a holding portion for holding the cover member and a fluid flow path for communicating the processing portion and the outside. At least a part of the fluid flow path is located on the side of the light source portion, and the light source portion and the flow path member are in thermal contact with each other. The flow path member has a mounting portion to which the light source portion is detachably mounted. [Selection diagram] Fig. 2【課題】光源の温度上昇を抑えつつ、部品の交換を容易にすることができる。【解決手段】実施形態の流体殺菌装置は、処理部と、光源部と、カバー部材と、流路部材とを具備する。処理部は、流体を処理する。光源部は、処理部に向けて紫外線を照射する光源と、光源を支持する支持部材とを有する。カバー部材は、光源部の前面側に配置され、光源を流体から保護する。流路部は、カバー部材を保持する保持部と、処理部と外部とを連通させる流体流路とを有する。流体流路の少なくとも一部は、光源部の側方に位置し、光源部と流路部材とが熱的に接触する。流路部材は、光源部が着脱可能に装着される装着部を有する。【選択図】図２
