A rotary compressor characterized by comprising: - a vertically-positioned airtight compressor housing having an upper section in which a discharge portion of a refrigerant is provided and a lower section in which an inlet unit of the refrigerant is provided on a side surface thereof; - a compressing unit that is disposed in the lower section of the compressor housing, that includes an annular cylinder (121S, 121T), an end plate (160S, 160T) which has a bearing unit (161S, 161T) and a discharge valve unit (190S, 190T, 200S, 200T, 201S, 201T) and closes an end portion of the cylinder, an annular piston (125S, 125T) which is fit in an eccentric portion (152S, 152T) of a rotation shaft supported in the bearing unit, performs an orbital motion inside the cylinder along a cylinder inner wall (123S, 123T) of the cylinder, and forms an operation chamber (130S, 130T) together with the cylinder inner wall, and a vane (127S, 127T) which protrudes from the inside of a vane groove (128S, 128T) of the cylinder to the inside of the operation chamber, comes into contact with the annular piston, and partitions the operation chamber into an inlet chamber (131S, 131T) and a compression chamber (133S, 133T), and that performs suction of the refrigerant via the inlet unit and discharges the refrigerant from the discharge portion via the inside of the compressor housing; and - a motor that is disposed in the upper section of the compressor housing and drives the compressing unit via the rotation shaft, wherein the vane (127S, 127T) is formed of steel and has a diamond-like carbon layer (127SD, 127TD) formed on a sliding surface with respect to the annular piston, and characterized in that the annular piston (125S, 125T) is formed of Ni-Cr-Mo cast iron to which 0.15 wt% to 0.45 wt% of phosphorus is added and has an iron nitride layer (125SN, 125TN) formed only on an outer circumferential surface thereof. - a vertically-positioned airtight compressor housing having an upper section in which a discharge portion of a refrigerant is provided and a lower section in which an inlet unit of the refrigerant is provided on a side surface thereof; - a compressing unit that is disposed in the lower section of the compressor housing, that includes an annular cylinder (121S, 121T), an end plate (160S, 160T) which has a bearing unit (161S, 161T) and a discharge valve unit (190S, 190T, 200S, 200T, 201S, 201T) and closes an end portion of the cylinder, an annular piston (125S, 125T) which is fit in an eccentric portion (152S, 152T) of a rotation shaft supported in the bearing unit, performs an orbital motion inside the cylinder along a cylinder inner wall (123S, 123T) of the cylinder, and forms an operation chamber (130S, 130T) together with the cylinder inner wall, and a vane (127S, 127T) which protrudes from the inside of a vane groove (128S, 128T) of the cylinder to the inside of the operation chamber, comes into contact with the annular piston, and partitions the operation chamber into an inlet chamber (131S, 131T) and a compression chamber (133S, 133T), and that performs suction of the refrigerant via the inlet unit and discharges the refrigerant from the discharge portion via the inside of the compressor housing; and - a motor that is disposed in the upper section of the compressor housing and drives the compressing unit via the rotation shaft, wherein the vane (127S, 127T) is formed of steel and has a diamond-like carbon layer (127SD, 127TD) formed on a sliding surface with respect to the annular piston, and characterized in that the annular piston (125S, 125T) is formed of Ni-Cr-Mo cast iron to which 0.15 wt% to 0.45 wt% of phosphorus is added and has an iron nitride layer (125SN, 125TN) formed only on an outer circumferential surface thereof.