PURPOSE: To form a cylinder block of a radial piston machine so that a front surface guide face for rollers is obtained in which all roller are well utilized as a support despite a simplified process of the block machining.

CONSTITUTION: This engine includes a ring-shaped cam plate 3 and a rotor installed rotatably around the shaft as a cylinder block 100. The engine further includes a number of inner holes 110 arranged in the radial direction to the rotary shaft of the cylinder block, a piston 120 movable inside the inner holes, cylindrical rollers 140 having an axis stretching parallel with the rotary shaft of the cylinder block and for supporting the piston on the cam plate, and a recess positioned inside the stroke region of the rollers 140 for receiving the roller sections of the front surfaces 141 and 142 of the rollers. Owing to guidance of the front surfaces of the rollers, the guide faces 103 and 104 for rollers positioned opposingly can be machined by a milling process.