PURPOSE: To improve the wear and abrasion resistance of a reciprocating compressor by dividing a piston fittedly provided in a cylinder into a piston ring attaching part and a rider ring part, and forming a cylinder inner wall face, where the rider ring part moves vertically, of material impregnated with lubricating oil.

CONSTITUTION: In an unlubricated reciprocating compressor, a piston is divided into a piston 2 fitted with a piston ring 1 and a piston 5 fitted with a rider ring 4, and the pistons 2, 5 are mutually connected through a rod 7. Each of the pistons 2, 5 is vertically slided in a cylinder 3 and a cylinder 6 made of oil impregnated material with the vertical movement of a connecting rod 8 connectingly provided on a crankshaft rotated by a prime mover. In this case, the piston 5 takes over side pressure acting on a piston to prevent the piston 2 from suffering from the side pressure for reducing the wear of the piston ring 1, and in addition, the rider ring 4 made of wear resisting material is used to improve the durability of the whole of the compressor.