To efficiently and with a few man-hours manufacture the tube with predetermined length, a thin diameter and high performance by forming semicircular semicircle parts on a pair of tabular stocks respectively, connecting both semicircle parts each other so that its cross-section becomes a circle, and joining both semicircle parts each other after fixing them temporarily.

Parts among the rows of through-holes 2 are worked on the tabular stock 1a by press working, etc. to the semicircle parts 5a with semicircular cross- sections, having desired curvatures and extending in the width direction of the stock 1a. Through-holes 6 consisting of square holes are punched on the tabular stock 1b as well in positions corresponding to the through-holes 2. The parts among the rows of the through-holes 6 are worked by press working, etc., to the semicircle parts 5b with the semicircular cross-sections, having desired curvatures and extending in the width direction of the stock 1b. The stocks 1a, 1b are connected, and the corresponding semicircle parts 5a, 5b are connected one another. Both side walls of the semicircle parts 5b facing to the semicircle parts 5a, are calked from the outside by projecting pieces 3 on both sides of these semicircle parts 5a, and the semicircle parts 5a, 5b are temporarily fixed.