PURPOSE: To execute deformation and increase of the tube wall thickness by supporting the tube wall except the part whose wall thickness is increased from the outside, and applying pressure to the tube wall part whose wall thickness is increased from the external surface from two directions orthogonal thereto while being heated in the plastic temperature range or locally.
CONSTITUTION: When the thickness of the wall part 1a of a tube 1 is increased, the tube 1 is place with on a support 3 to be supported by a U-shaped frame 2 with the wall part 1a upside. Squeeze members 6, 7 mounted on the tip of the piston, of hydraulic cylinders 4, 5 which are similarly supported by the frame 2 are abutted on the external side of the tube walls 1c, 1d. The tube wall 1a is locally heated through an abutting member 8 by a high frequency heating inductor 9 which is connected to the power source 10, and the compressive force is applied from the sides 1c, 1d by means of the squeeze members 6, 7 while the temperature being risen to the plastic temperature range of the tube material. This compressive force allows the deformation and increase in the thickness of the part whose tube wall thickness is increased, and the wall-thickened part is heated.