A radial piston hydraulic machine comprising: at least one cylinder having an inner wall; at least one piston provided reciprocably in the at least one cylinder, respectively; a cam having a cam surface formed by a plurality of lobes arranged along a circumferential direction of the hydraulic machine, the cam being configured rotatably so that the plurality of lobes moves relative to each of the at least one piston in the circumferential direction; and at least one roller rotatably engaging with the at least one piston, respectively, the at least one roller contacting the cam surface, each of the at least one cylinder is arranged inclining with respect to a radial direction of the hydraulic machine to satisfy a relation of 0 < X < Y, where X is an angle between a center axis of each of the at least one cylinder and a first line connecting a center of said each of the at least one roller and a center of the cam in such a state that each of the at least one roller is in contact with a vertex point of the lobe, and Y is an angle between a normal line of the cam surface at an inflection point (Zinf) of the cam surface between a bottom point and the vertex point of the lobe and a second line connecting the center of the cam and the inflection point (Zinf), each of the at least one piston includes a first section having a pressure receiving surface for receiving pressure from operating oil in a hydraulic chamber formed by each of the at least one cylinder and each of the at least one piston, and a second section disposed closer to the cam than the first section and engaging with the at least one roller; and a stepped portion is disposed between the first section and the second section such that a width of the second section along a rotational direction of the cam is greater than a diameter of the first section; and characterized in that the second section and the inner wall of the cylinder facing the second section are configured to receive a side force along a rotational direction of the cam. at least one cylinder having an inner wall; at least one piston provided reciprocably in the at least one cylinder, respectively; a cam having a cam surface formed by a plurality of lobes arranged along a circumferential direction of the hydraulic machine, the cam being configured rotatably so that the plurality of lobes moves relative to each of the at least one piston in the circumferential direction; and at least one roller rotatably engaging with the at least one piston, respectively, the at least one roller contacting the cam surface, each of the at least one cylinder is arranged inclining with respect to a radial direction of the hydraulic machine to satisfy a relation of 0 < X < Y, where X is an angle between a center axis of each of the at least one cylinder and a first line connecting a center of said each of the at least one roller and a center of the cam in such a state that each of the at least one roller is in contact with a vertex point of the lobe, and Y is an angle between a normal line of the cam surface at an inflection point (Zinf) of the cam surface between a bottom point and the vertex point of the lobe and a second line connecting the center of the cam and the inflection point (Zinf), each of the at least one piston includes a first section having a pressure receiving surface for receiving pressure from operating oil in a hydraulic chamber formed by each of the at least one cylinder and each of the at least one piston, and a second section disposed closer to the cam than the first section and engaging with the at least one roller; and a stepped portion is disposed between the first section and the second section such that a width of the second section along a rotational direction of the cam is greater than a diameter of the first section; and characterized in that the second section and the inner wall of the cylinder facing the second section are configured to receive a side force along a rotational direction of the cam.