PURPOSE: To easily form a perforated tube of sheet metal which is spirally coiled by continuously perforating a strip in the length direction, feeding it obliquely to the axis of a mandrel and rotating the the mandrel around the axis.

CONSTITUTION: By bending the edges of the strip with the rollers of a unit 4, an upward flange and downward flange are respectively formed and, by bending them with the rollers 160, 162, hooks are formed. The cylindrical mandrel 10 is set at a certain angle to the direction of the arrow 6 and rotated around the axis. Under the mandrel 10, a 1st deflector plate 14 is arranged and the 2nd deflector plate 16 having a concave bottom is arranged obliquely above the mandrel. A seam forming roller 18 is mounted under the mandrel and the edges with the flange of the strip are fixed together. To cut the tube at right angle to the axis, the edge on the circumference which cooperates with a cutter mounted on the frame 22A around an end 20 for planetary motion is provided with the end 20, a series of the length part of a regular cylindrical tube is formed.