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 , an end plate which has a bearing unit and a discharge valve unit and closes an end portion of the cylinder, an annular piston which is fit in an eccentric portion of a rotation shaft supported in the bearing unit, performs an orbital motion inside the cylinder along a cylinder inner wall of the cylinder, and forms an operation chamber together with the cylinder inner wall, and a vane which protrudes from the inside of a vane groove 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 and a compression chamber , 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 is formed of steel and has a diamond-like carbon layer formed on a sliding surface with respect to the annular piston, and characterized in that the annular piston 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 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 , an end plate which has a bearing unit and a discharge valve unit and closes an end portion of the cylinder, an annular piston which is fit in an eccentric portion of a rotation shaft supported in the bearing unit, performs an orbital motion inside the cylinder along a cylinder inner wall of the cylinder, and forms an operation chamber together with the cylinder inner wall, and a vane which protrudes from the inside of a vane groove 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 and a compression chamber , 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 is formed of steel and has a diamond-like carbon layer formed on a sliding surface with respect to the annular piston, and characterized in that the annular piston 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 formed only on an outer circumferential surface thereof. <EOS>