FLUID STERILIZATION DEVICE

A fluid sterilization device includes a cylindrical body of a housing having a flow passage through which fluid flows in an axial direction, an inflow port through which the fluid flows into the cylindrical body, an outflow port on the outer circumference of the cylindrical body, a light source provided on an end section on an opposite side to the inflow port, and a quartz cap including a cylindrical section and a leading end section. The quartz cap transmits, collects, or scatters ultraviolet light. The cylindrical section of the quartz cap is fitted to an inner wall of the cylindrical body, and a boundary section of the quartz cap is disposed a position coinciding with an end surface of the outflow port on a side close to the first light source or at a position where the boundary section protrudes beyond the end surface.