PURPOSE: To shorten the time for production of a tubular member by forced feeding fluid between both tubes after bending a workpiece, then expanding the tube on an outer side in at least a portion in a longitudinal direction.

CONSTITUTION: The double walled tubular member having a stable shape which is at least partly bent and is provided with an intermediate space in one portion in a longitudinal direction is produced. The tube 3 for forming the wall on the inner side is inserted into the tube 5 for forming the wall on the outer side and the workpiece 1 produced at this time is at least partially bent. After the workpiece 1 is, thereupon, bent, the fluid 79 is force bed between both tubes 3 and 5, and the tube 5 on the outer side is expanded at least in one portion in the longitudinal direction. A fluid source 75 for force feeding the fluid 79 between both tubes is disposed. As a result, the mass production of the tubular member may be implemented automatically, i.e., without requiring manual work, by using simple appliances.