An accumulator capable of suppressing collision of a metal bellows with a pressure vessel. A partition unit 300 includes: a tubular metal bellows 310, one end of which is side fixed to a pressure vessel 200 and which expands and contracts according to pressure in a fluid chamber and pressure in a gas chamber; and a bellows cap 320 which is fixed to another end side of the metal bellows 310, the partition unit 300 further including: a seal member 330 which is provided between the bellows cap 320 and a port 221 and seals a working fluid on the side of the fluid chamber via the metal bellows 310 when the metal bellows 310 contracts; and a sliding unit 350 which is fixed to the bellows cap 320 and slides in an expansion/contraction direction of the metal bellows 310 relative to a stay 400.