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 (G) containing a gas sealed therein, and a fluid chamber (L) 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 (G) and the pressure in the fluid chamber (L), 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 (S) 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 (G) containing a gas sealed therein, and a fluid chamber (L) 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 (G) and the pressure in the fluid chamber (L), 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 (S) 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 (S) between the metal bellows and the trunk part , regardless of an expanded or contracted state of the metal bellows . <EOS>