PURPOSE: To provide an apparatus for forming tubes into coils and welding the coils together and a method therefore in production of a vessel of which the side wall is formed of a cylindrical body obtd. by adjacently winding the tubes to the coils and welding their top contact parts together.

CONSTITUTION: A mandrel 20 supported by a chuck 22 and a tailstock 24 is installed on a frame 18 and is driven by a gear speed reducer 26 driven by an electric motor 28 as a driving power source. A carriage 30 is arranged to enclose the upper part of the mandrel and is driven by a rod 36 of a hydraulic cylinder 34. A tension device 46 is fixed to the carriage and the tube 16 is securely wound by rotation of the mandrel. A welding torch 50 is mounted at the carriage to join the top contact parts of the coiled tube 48. The coil is removed together with the mandrel from the device in the stage when the joining of the vessel wall having a prescribed length ends. The mandrel is then destroyed and removed, by which the vessel side wall is produced.