A compressor having a front housing in which a crank chamber is formed. A cylinder block is coupled to an opposite surface facing the front housing and includes reciprocating pistons in a plurality of cylinder bores. A rear housing is coupled to an opposite surface facing the cylinder block, the rear housing includes a suction chamber and a discharge chamber formed therein. A rotating shaft 400 is inserted via centers of the front housing and the cylinder block, the shaft inserted into a swash plate. A diameter maintenance part is configured to constantly maintain a diameter based on an axis direction of the piston 220. A sensor part is configured to sense a speed and a stroke of the piston in accordance with a change in position of a position determination part positioned on one side of the diameter maintenance part.