In a hydraulic rotary machine having rotational shaft provided within a casing a rotational shaft, a cylinder block rotationally interlocked with the rotational shaft and formed with a plural number of cylinder bores, and pistons slidably received in the cylinder bores and adapted to slide back and forth within the cylinder bores while the rotational shaft and the cylinder block are put in rotation in synchronism with each other, a multitude of minute pits are formed at least either on sliding surfaces on the side of the cylinder bores, each one of the minute pits are in an elliptical shape defining a moderately sloped surface in one side and an acutely sloped surface in the other side, and the moderately sloped surfaces of the minute pits are oriented to face a direction in which said pistons are put in sliding movement in said cylinder bores under a greater load than in the other direction.