A fluid sterilizing device (1) includes barrel portion (5) having a channel where fluid to be sterilized flows； inlet (6a) formed on one end portion side of the barrel portion (5)； outlet (7a) formed on the other end portion side of the barrel portion (5)； a light source (3) that emits ultraviolet light toward the fluid； and a rectifier (12) mounted inside the channel and having a cylindrical through hole. The rectifier (12) includes inner circumferential region Rin expanding from its center in the diameter direction of the channel, and outer circumferential region Rout expanding outside the inner circumferential region Rin. The ratio (t/d)out of the panel thickness t relative to the diameter d of each through hole in the outer circumferential region Rout is larger than the ratio (t/d)in of the panel thickness t relative to the diameter d of each through hole in the inner circumferential region Rin.
