A fluid sterilization device includes a straight pipe that constitutes a flow passage extending in a longitudinal direction, and a light source that emits ultraviolet light in the longitudinal direction toward a fluid flowing in a laminar state within the flow passage. The light source includes a light emitting element 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.
