A fluid sterilization device 10 includes a straight pipe 20 that constitutes a flow passage 12 extending in a longitudinal direction, and a light source 40 that emits ultraviolet light in the longitudinal direction toward a fluid flowing in a laminar state within the flow passage 12. The light source 40 includes a light emitting element 42 for emitting ultraviolet light and emits ultraviolet light so as to provide an intensity distribution on a cross section of the flow passage perpendicular to a longitudinal direction, in which the ultraviolet intensity in an area near the center is higher than the ultraviolet intensity around the area.
