Patent ID: 8241496

Claim:
A filter device comprising: a casing having an inlet for introducing fluid and an outlet for discharging fluid; a filtering element disposed between the inlet and the outlet of the casing, wherein fluid passes through the inlet, the filtering element, and the outlet in this order; and a compressing portion compressingly contacting the filtering element, wherein the filtering element has an outer circumference face extending in a fluid flowing direction, the outer circumference face of the filtering element has a hardened part produced by hardening only a surface of the filtering element and being integrated with a non-hardened part of the filtering element disposed on an inner side of the hardened part, the filtering element has an upstream end face on an upstream end in the fluid flowing direction, and a downstream end face on a downstream end in the fluid flowing direction, the compressing portion has a curved contact surface protruding toward the upstream end face, the filtering element is compressed in the fluid flowing direction by the compressing portion compressingly contacting the downstream end face, and the hardened part of the outer circumference face of the filtering element maintains an outer peripheral dimension of the filtering element approximately uniform between the upstream end face and the downstream end face when the compressing portion compressingly contacts the downstream end face to compress the filtering element in the fluid flowing direction.