The present invention provides an ultraviolet light irradiation device having high robustness, and configured to prevent leakage of a fluid to be sterilized, even though assembly precision is not sufficiently high.A fluid sterilization module (1) includes an inner cylinder (21), a case portion (22) in which the inner cylinder (21) is accommodated, a member (24) provided in close contact between an outer circumferential surface of the inner cylinder (21) and an inner circumferential surface the case portion (22), a first chamber (26) located in a region on a side of one end portion of the inner cylinder (21) with respect to the member (24), in a cylindrical gap between the inner cylinder (21) and the case portion (22), a second chamber (27) located in a region on a side of the other end portion of the inner cylinder (21) with respect to the member (24), an inflow portion (4) through which an object flows into the first chamber (26), an outflow portion (5) through which the object flows out of the second chamber (27), and a light emitting element (34a) provided in at least one of the one end portion and the other end portion of the inner cylinder (21), and configured to emit ultraviolet light to the object passing through a processing flow path (21d).
