PURPOSE: To improve the productivity and yield of a slow-wave circuit for a travelling-wave tube by engaging a plurality of support rods in a plurality of engagement grooves for positioning surely at a high efficiency, and charging brazing material to brazing material supply positions so as to increase the brazing efficiency and the reproducibility.

CONSTITUTION: Support rods 2 are equally disposed around a helix coil 3, and they are fixed at brazing parts 5. The support rods 2 are engaged in equally disposed grooves 8 of a rectangular sectional form in the inner wall of a main body of a metal pipe 7 to be positioned, and then linear brazing material 4a is charged to grooves 9. The main body 7 is heated to fuse the brazing material 4a, it is then cooled and solidified, so the pipe 1 is connected with the support rods 2. In/out terminals 10, 11 are introduced from guide holes 12, 13, and they are brazed to the coil 3. In this constitution, the assembling precision is greatly improved, and brazing material can be supplied easily in a desired quantity with a good reproducibility, which improves the reliability of brazing, thereby the productivity and yield of a slow-wave circuit for a travelling-wave tube can be improved.