To increase an upper limit of pressure condition capable of suppressing friction with an inner peripheral member to the small extent while keeping satisfactory sealing property.

A first seal ring 20 and a second seal ring 30 arranged in a non-rotation condition are provided on a high pressure space H side of an annular end wall part 12 in which the inner peripheral member 80 is inserted. The first seal ring 20 is constituted such that a first segment 21 is annularly combined with a clearance in the circumferential direction and is elastically bound by a garter spring 22 so that it adheres closely to an outer peripheral face of the inner peripheral member 80. The second seal ring 30 is energized in the axial direction by a compression spring 40 through the first seal ring 20 so that one end face 31c adheres closely to the end wall part 12 and it has a clearance G2 between the inner peripheral face and the outer peripheral face of the inner peripheral member 80. Pressure balance grooves 21c, 21d opened onto the high pressure space H side are formed on an inner peripheral face of the first segment 21.