An accumulator includes a bellows 3 having a plurality of outer ridge portions and a plurality of inner annular ridge portions and configured to be capable of expanding and contracting, and a housing having a fluid supply port and fixed to one end of the bellows serving as a fixed end. An interior of the housing is partitioned in a sealed state into an inside and an outside of the bellows. The outer annular ridge portions are divided into at least a first sector and a second sector which are distributed in an expansion and contraction direction of the bellows such that the second sector is positioned between the first sector and the fixed end. The outer annular ridge portions included in the first sector have an outer diameter smaller than an outer diameter of the outer annular ridge portions included in the second sector.