NOVELTY - The accumulator (1) has a sealing element (31) that is maintained through seal holder (21) at port hole (5) side of bellows cap (10), and is moved with bellows cap during regular operation. The sealing element contacts seal portion (15) provided in inside of housing (2), and occludes hydraulic chamber (12). The sealing element adheres flexible portion (34) which becomes outer peripheral surface of rigid plate (32) from elastomeric portion. The relative displacement of the bellows cap is permitted when flexible portion carries out shearing deformation by engagement with seal holder.    USE - Accumulator used as pressure accumulation apparatus or pulse-pressure attenuation device for hydraulic piping in vehicle e.g. motor vehicle.    ADVANTAGE - Since the sealing element made is a rigid plate, the outer circumferential surface of rigid plate is covered by a flexible section obtained from a rubber-like elastic portion, and the flexible section allows relative movement of the bellows cap by undergoing shear deformation as a result of engagement with the seal holder. The length dimension of a seal holder is shortened to make components small, so that spring element is avoided and number of components is avoided. The shearing deformation is easily carried out when a flexible portion engages with a seal holder by setting the outside diameter size of a flexible portion more largely than the internal diameter size of a flange portion. The relative displacement amount with a sealing element, a seal holder, and a bellows cap is increased by providing outer periphery protrusion and a groove in a flexible portion. The pressure difference is reduced rapidly even when the pressure difference which generates when the liquid and filler gas which are sealed by the hydraulic chamber at the time of a zero down thermally expand is big. The sealing performance is fully securable by providing seal protrusion in rigid plate. The manufacture process of components is facilitated by molding seal protrusion and a flexible portion integrally.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of an accumulator.    Accumulator (1)    Housing (2)    Port hole (5)    Hydraulic chamber (12)    Seal portion (15)    Seal holder (21)    Sealing element (31)    Rigid plate (32)    Flexible portion (34)