To provide an accumulator which is capable of relieving a pressure in a seal attaching portion (a portion under a seal) in order to make the attached state of a seal stable and prevent slipping off of the seal from the seal attaching portion, the seal attaching portion with which a working member is freely contacted and released and a seal holder attaching portion attaching a seal holder holding the seal are provided around a pressure inflow port inside the inner surface of a housing receiving the working member such as a bellows cap, the seal is attached to the seal attaching portion, the seal holder is attached to the seal holder attaching portion by fixing means such as welding, bonding, screwing, engaging, or fitting, and a pressure relief path is provided for relieving the pressure in the seal attaching portion generated by attaching of the seal thereon.