A fluid sterilization apparatus 20 includes: a flow passage tube 22 in which a processing passage 36 where a passing fluid is sterilized is formed； a first light source 28 that irradiates the processing passage 36 with ultraviolet light； an inflow passage 42b formed in a direction that intersects an outer circumferential surface 22c of the flow passage tube 22； and a communication passage 78 that causes the inflow passage 42b to communicate with the processing passage 36. The communication passage 78 has a narrow passage 80 in the middle of a path from the inflow passage 42b toward an opening 22d of a first end 32, the narrow passage 80 being narrower than a passage toward the inflow passage.
