To appropriately control quantity of the blowby gas, while preventing corrosion of a piston.

This piston 18 for a compressor is connected to a driving mechanism through a connection part 18B inside of a crank chamber 5, reciprocated inside of a cylinder bore 3, and used for a compressor 60, having a process for compressing the coolant gas sucked into the cylinder bore 3 accompanying the reciprocating motion, Coating is performed on the peripheral surface of a cylindrical piston body 18A, and the surface of a formed coating layer 18F is provided with a groove part 18G which is within the thickness range of the coating layer. By installing this structure, corrosion of the piston body 18A is prevented, and released of limitation of the coolant gas, the lubricating oil and the material; each member of the crank chamber 5 side is lubricated and cooled by the lubricating oil included in the blowby gas from the groove part 18G; furthermore, seizure and abrasion is prevented by the lubricating and cooling effects of the lubricating oil supplied from the groove part 18G to a part between the piston body 18A and the cylinder bore 3; and durability is improved.