A damper comprising a piston provided with a rod, and a housing storing the piston, and generating a braking force by an operation of the piston, wherein the piston includes a seal member relative to an inner wall of the housing, and a slider provided slidably relative to the piston, and contacting the inner wall of the housing with a predetermined frictional force, and when the braking force is generated, the slider presses against the seal member, so that a portion contacting the inner wall of the housing in the seal member deforms outwardly toward the housing, characterized in that the piston is provided with a first flange facing a blocking end of the housing; and a second flange retaining the seal member and the slider between the second flange and the first flange, wherein the second flange is positioned at a back side of the first flange, i.e. on an open end side of the housing, wherein in both the first flange and the second flange, an outer frame shape in a cross section in a moving direction (x) of the piston, i.e. in a direction orthogonally in a direction along the cylinder shaft of the housing, has a shape which becomes a complementary shape to an inner frame shape in the cross section of the housing in the same direction, thereby the piston is guided by the inner wall of the housing so as to reciprocate in the direction along the cylinder shaft of the housing, the slider is provided with a short cylindrical base, the seal member includes a front end face relative to a first flange; an inner face relative to an outer face of a head part; and an outer face relative to the inner wall of the housing, wherein on a side facing an open end side of the housing in the seal member, there is formed a circumferential groove between the inner face and the outer face, wherein an outer face side sandwiching the circumferential groove extends toward the open end side of the housing throughout all circumferential directions of the seal member, so that the seal member is provided with a skirt-shaped portion, and the outer face of the seal member increases a size more than the inner face in a moving direction (x) of the piston, wherein a lip integrally formed outside the base of the slider has a base portion integrated with an outer face portion of a base between a front end positioned on a seal member side and a back end positioned on the open end side of the housing in the base, and is provided with an extension portion extending toward the open end side of the housing from the base portion, a shoulder portion is formed between the base portion and the extension portion, the extension portion has inclination gradually increasing a distance between the extension portion and the base as moving to a terminal thereof from the shoulder portion, wherein the outer face of the seal member inclines in a direction of gradually increasing a thickness of the seal member as moving from the front end face to a terminal of the skirt-shaped portion, wherein the seal member and the slider are held between the first flange and the second flange in a state allowing a slight movement along the moving direction (x) of the piston, wherein the outer face of the seal member contacts the inner wall of the housing throughout a whole circumference thereof, and the extension portion of the slider contacts the inner wall of the housing on a terminal side thereof throughout a whole circumference thereof as well, wherein a portion located between the front end of the base of a slider and the base portion of a lip is positioned inside the skirt-shaped portion of the seal member, and the shoulder portion of the lip of the slider faces the terminal of the skirt-shaped portion of the seal member.