A piston-type accumulator has: a) an accumulator housing in the form of a cylinder tube (1) made of magnetizable material, which defines an axial direction of the housing; b) a piston (3), which can be axially displaced over a stroke path inside the cylinder tube (1) and which forms a moving separating element that, inside the accumulator housing, separates two working spaces (7 and 9) from one another; c) a magnet arrangement (29, 31, 35), placed on the piston (3) and generating a field on the wall of the cylinder tube (1), and; d) a magnetic field sensor device located on the exterior of the cylinder tube (1) and having at least one Hall sensor (51). The Hall sensor is mounted on the exterior of the cylinder tube (1) and responds to the field generated by the magnet arrangement (29, 31, 35) on the piston (3) to determine the position of the piston (3) along the stroke path.