To obtain certain sealability by the contact of a valve disc with a valve seat part while ensuring the filtering area of a filter element without complicating a structure.

When the pressure of the oil flowing in from the oil inlet 25 of the case 20 of an oil filter 100 becomes predetermined pressure or more, the valve disc part of a relieve valve 50 is operated and the oil is permitted to pass without being passed through a filter element to be allowed to escape to an oil outlet 26. The relief valve 50 is arranged by utilizing the space in the filter element 31 and the filtering area of the filter element 31 can be ensured without increasing the vol. of the oil filter 10. Since the relief valve 50 is set to a line seal state by the planar line contact of the valve disc part thereof with the opposed valve seat part 35d, certain sealability can be obtained.