An accumulator, comprising: a pressure vessel; and a partition unit provided in the pressure vessel, and partitioning an internal space thereof into a gas chamber containing a gas sealed therein, and a fluid chamber containing a working fluid flowing therein, the partition unit including a metal bellows to be expanded and contracted according to the pressure in the gas chamber and the pressure in the fluid chamber, the metal bellows including a plurality of annular crest parts and a plurality of annular valley parts alternately formed therein, a damping member (190; 190X) formed slidably at an inner circumferential surface of the pressure vessel and suppressing the oscillation of the metal bellows while keeping a gap between the metal bellows and the inner circumferential surface of the pressure vessel, the damping member (190; 190X) being mounted at at least one site of the plurality of annular valley parts of the metal bellows, wherein in the damping member (190; 190X), a radially inward tip is fitted with the valley part, and a radially outward tip is longer than the crest part of the metal bellows radially and outwardly, and the damping member (190; 190X) includes: a trunk part extending in the circumferential direction, and a fitted part provided on the radially inward side of the trunk part, and fitted with the valley part, characterized in that the damping member (190; 190X) is positioned and fixed at the metal bellows so as to form a gap between the metal bellows and the trunk part, regardless of an expanded or contracted state of the metal bellows. a pressure vessel; and a partition unit provided in the pressure vessel, and partitioning an internal space thereof into a gas chamber containing a gas sealed therein, and a fluid chamber containing a working fluid flowing therein, the partition unit including a metal bellows to be expanded and contracted according to the pressure in the gas chamber and the pressure in the fluid chamber, the metal bellows including a plurality of annular crest parts and a plurality of annular valley parts alternately formed therein, a damping member (190; 190X) formed slidably at an inner circumferential surface of the pressure vessel and suppressing the oscillation of the metal bellows while keeping a gap between the metal bellows and the inner circumferential surface of the pressure vessel, the damping member (190; 190X) being mounted at at least one site of the plurality of annular valley parts of the metal bellows, wherein in the damping member (190; 190X), a radially inward tip is fitted with the valley part, and a radially outward tip is longer than the crest part of the metal bellows radially and outwardly, and the damping member (190; 190X) includes: a trunk part extending in the circumferential direction, and a fitted part provided on the radially inward side of the trunk part, and fitted with the valley part, characterized in that the damping member (190; 190X) is positioned and fixed at the metal bellows so as to form a gap between the metal bellows and the trunk part, regardless of an expanded or contracted state of the metal bellows. a trunk part extending in the circumferential direction, and a fitted part provided on the radially inward side of the trunk part, and fitted with the valley part, characterized in that the damping member (190; 190X) is positioned and fixed at the metal bellows so as to form a gap between the metal bellows and the trunk part, regardless of an expanded or contracted state of the metal bellows.