PURPOSE: To obtain various reversal shapes by smooth and easy reversal operation by a method wherein a concal projection part having a curved surface groove formed to the periphery thereof is inserted in the opening end of a pipe and a guide part is continuously advanced and rotated to reverse the opening end of the pipe.

CONSTITUTION: A rotary shaft 7 is rotated by a motor 7 and, when a handle 11 is rotated in a predetermined direction at the point of time when a guide part 3 having a curved surface groove 36 comes into contact with the opening end of a pipe P, an advance and retreat shaft 8 is moved forwardly in the direction shown by an arrow (a). By this constitution, a housing 9 presses the rotary shaft 4 through a bearing part 10 to integraly operate a cylindrical gear 5, a gear 6 and the motor 7 freely slidable along the bottom surface of a case C. When the guide part 3 is pressed to the pipe P under rotation, the opening end of the pipe P is guided by the curved surface groove 36 of the guide part 3 in spite of extremely small pressing force to be guided to the outside and reversed at last to become the state fitted to the outer periphery of a ring R.