A cylinder block for the two-cycle combustion engine includes a scavenging port open at an inner peripheral surface of the cylinder block so as to orient diagonally upwardly relative to a longitudinal axis of a cylinder bore and defined in the cylinder block in communication with a combustion chamber. This scavenging port is formed by cutting with the rotary cutting tool, then rotated about its own longitudinal axis, from an inner peripheral surface of the cylinder block.