A piston-type accumulator comprises: a) an accumulator housing provided 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), which is placed on the piston (3) and which generates a field on the wall of the cylinder tube (1), and; d) a magnetic field sensor device, which is located on the exterior of the cylinder tube (1) and which has at least one Hall sensor (51). Said 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) in order to determine the position of the piston (3) along the stroke path.