A piston accumulator (10) comprises a pressure chamber (40) which on one side is closed by a piston (50) axially displaceable in a pipe (20) in order to change its volume depending on the axial position of the piston (50). A detent mechanism is provided in order to hold back the piston (50) against a spring preload (190) in a second position differing from a first position. The piston (50) is formed in a multi-part fashion and comprises at least a first piston part (52) and a second piston part (54), wherein at least one of the two piston parts (52) is hardened and disposed to cooperate with the detent mechanism in a catching fashion.