A bent axis type hydraulic rotating machine comprising: - a tubular casing; - a rotational shaft rotatably disposed in said casing; - a cylinder block which is provided in said casing to rotate together with said rotational shaft and provided with a plurality of cylinder holes to be spaced in the circumferential direction and axially extend; - a plurality of tapered pistons each of which includes a tapered shaft portion formed to be enlarged in a tapered shape from one end side toward the other end side in an axial direction, - a spherical portion formed integrally with one end side of said tapered shaft portion, and - a piston portion formed in the other end side of said tapered shaft portion, and pivotably supported on said rotational shaft at said spherical portion side thereof and reciprocally inserted into each of said cylinder holes of said cylinder block at said piston portion side thereof; and - a valve plate which is provided between said casing and said cylinder block and in which a pair of supply and discharge ports (13B, 13C) communicating with each of said cylinder holes are formed, wherein one of the pair of said supply and discharge ports (13B, 13C) serves as a high-pressure side supply and discharge port, and the other serves as a low-pressure side supply and discharge port, each of said plurality of cylinder holes of said cylinder block has an opening peripheral edge for inserting said plurality of tapered piston into each of said plurality of cylinder holes, said plurality of tapered piston makes contact with said opening peripheral edge of each of said plurality of cylinder holes in a constant section in which each of said plurality of cylinder holes is communicated with said low-pressure side supply and discharge port and in a constant section in which each of said plurality of cylinder holes is communicated with said high-pressure side supply and discharge port while said cylinder block rotates one revolution, a nitriding layer, which is formed by executing nitride-based treatment together with each of said plurality of cylinder holes, is formed in said cylinder block, characterized in that: said nitriding layer is being configured to be constituted by a diffusion layer formed on a surface side of a base material and a compound layer formed on a surface side of said diffusion layer, and a chemical conversion film being configured to be composed of a manganese phosphate film is formed on a surface side of said diffusion layer of said nitriding layer from which said compound layer is removed by abrasive means, at each of said plurality of cylinder holes of said cylinder block. - a tubular casing; - a rotational shaft rotatably disposed in said casing; - a cylinder block which is provided in said casing to rotate together with said rotational shaft and provided with a plurality of cylinder holes to be spaced in the circumferential direction and axially extend; - a plurality of tapered pistons each of which includes a tapered shaft portion formed to be enlarged in a tapered shape from one end side toward the other end side in an axial direction, - a spherical portion formed integrally with one end side of said tapered shaft portion, and - a piston portion formed in the other end side of said tapered shaft portion, and pivotably supported on said rotational shaft at said spherical portion side thereof and reciprocally inserted into each of said cylinder holes of said cylinder block at said piston portion side thereof; and - a valve plate which is provided between said casing and said cylinder block and in which a pair of supply and discharge ports (13B, 13C) communicating with each of said cylinder holes are formed, wherein said nitriding layer is being configured to be constituted by a diffusion layer formed on a surface side of a base material and a compound layer formed on a surface side of said diffusion layer, and a chemical conversion film being configured to be composed of a manganese phosphate film is formed on a surface side of said diffusion layer of said nitriding layer from which said compound layer is removed by abrasive means, at each of said plurality of cylinder holes of said cylinder block.