PURPOSE: To manufacture the titled duct with a low cost and a high accuracy, by continuously connecting unit blocks having thin long hole at the cross-section with thier longer sides and welding the joint with electron beam.

CONSTITUTION: Unit blocks 1 having thin long hole 1a at the cross-section are placed so that the longer side may be contacted with the longer side of another block, and joint 2 between blocks as well as joint 2 between the block and side plate 3 at the both sides are welded with electron beam. Since unit block 1 and side plate 3 are welded with electron beam, they will be slightly deformed, but the sectional area of thin long hole 1a of unit block 1 will be unchanged. Thus highly accurate ducts for example, for liquid helium, are obtained.