A piston displacement device for a reciprocating compressor comprises a piston linearly reciprocated in a cylinder and having a stroke length varied by a reciprocating motor, a plurality of resonance springs for guiding a resonant motion of the piston, and a piston transfer unit for moving the piston forward or backward in a motion direction of the piston according to a capacitance variation of a compressor and thereby maintaining the same top dead center. The piston is moved according to a capacitance variation of the compressor thereby to minimize a dead volume thereof and to increase the efficiency of the compressor.