To provide a method for manufacturing a heat insulating waveguide simply even if the cross section of a waveguide to be formed is small and the length of the waveguide is long.

A metal rod 50 is provided, which has a section in the same shape as the contour of the section of the waveguide 4004 to be formed. A metal material having high waveguide efficiency is adhered onto the external surface of the rod 50 for forming a thin-film body 40 covering the external surface of the rod 50. On the external surface of the thin-film body 40, a metal cylinder 30 for reinforcing the thin-film body 40 is formed with a metal material having low thermal conductivity. A cylinder 20 made of a synthetic resin is formed, where the cylinder 20 adheres onto the external surface of the metal cylinder 30 for covering the metal cylinder 30 and has sufficient strength for retaining the shapes of the thin-film body 40 and the metal cylinder 30. The mutually integrated rod 50, the thin-film body 40, the metal cylinder 30, and the cylinder 20 made of a synthetic resin are dipped into an agent, and the rod 50 is dissolved for obtaining the heat insulating waveguide 10.