In a piston unit of a fluid pressure cylinder a plurality of magnets are disposed through holes provided in a ring body. The magnets are disposed in facing relation to detection sensors that are mounted on connecting rods, and are provided in the same quantity as the connecting rods. Further, a guide rod extending from a head cover to a rod cover is inserted through the interior of the ring body. When the piston unit is displaced along the cylinder tube, rotational displacement is restricted by the piston unit being displaced along the guide rod, whereby the magnets are retained to face toward the connecting rods at all times. Therefore, the position of the piston unit is detected by the detection sensors through the magnets.