PURPOSE: To obtain the titled light, flexible and strong heat exchanging tube that need not onsert turbulent piece by a method wherein spiral blades as turbulent piece are provided in a unitary body with the inner wall of the cylinder.

CONSTITUTION: As an inner mouth metal 24 is rotated, resin in the from of a plate is extruded downward from an extruding slit 30. From the extruding hole 36 of an outer mouth metal 26 resin is extruded downward in the cylindrical form as if resin extruded in the plate form is encircled. Above a cooling water tank 38 a cylindrical resin inner wall and a plate resin edge are butted, fixed and cooled in the cooling water tank 38 to be taken out. The plate resin is twisted spirally between the fixing position to the cylindrical resin inner wall and the inner mouth metal 24 and formed into the desired spiral blade. The turbulents do not oscillate in the flow direction and do not revolve around the axial line. Turbulent efficiency is improved and abnormal noises can be prevented from occurring.