To shorten working time by increasing forming speed without generating buckling when reducing the diameter in the end part of a metallic pipe.

In a forming method, a plurality of ring-like tools 11, 12 which have axial centers 11a, 12a parallel to the axial center 1a of the metallic pipe 1 the end part of which is reduced, the inner peripheries of which are brought into contact with the outer periphery of the metallic pipe and which are rotated are arranged in the radial direction of a frame 31 and, after arranging respective ring-like tools so that the inner peripheries do not be brought into contact with the outer periphery of the metallic pipe and also the metallic pipe is inserted, the end part of the metallic pipe is reduced by isolating the axial centers of the ring-like tools from the axial center while rotating the frame and also moving the metallic pipe or the ring-like tools.