An oil filter is provided which comprises a housing main body, a cover attached to the housing main body on the lower side thereof, an inner tubular member axially movably disposed in a recessed portion of the housing main body, a seal member interposed between the inner tubular member and the cover so as to provide a seal therebetween, a biasing unit for urging the inner tubular member in the direction to protrude from the recessed portion, and a filter element disposed in an oil flowing space between the housing main body and the cover, wherein when the cover is in a sate of being attached to the housing main body, the inner tubular member is pushed down into the recessed portion of the cover against a bias of the biasing unit.