To realize compactification and weight reduction of an oil filter by solving the problem, wherein upsizing and weight increase of the device are caused by an increase in an outer diameter of a cover part by a sealing member arranged the an outer peripheral side of a case, because the sealing surface provided between the case and the cover part is provided on the outer peripheral side of the case.

A set plate 20 is mounted on an opening part of the case 1, formed into a bottomed cylindrical shape and a ring body part 33 is fastened with the surrounding of an outer peripheral part 21 of the set plate 20 and is integrated in a state of a ring member 30, fitted into the surrounding of a body part 5 and the shoulder part 32 abutted on an outward flange 7 which is formed at an opening end of the body part 5. At this time, a seal support part 25 is provided at the inside of the body part 5 of the set plate 20. By mounting an O-ring 27 on the seal support part 25, the O-ring 27 is sealed, by bringing the O-ring 27 into close contact with an internal surface side of a general shape part of the body part 5.