To provide a method by which a dielectric line can be efficiently manufactured with high reliability and accuracy.

A resist material 22 is formed on a green molded body 23, an eroding step is performed by a sandblast method by using the resist material 22 as a mask, and a prescribed portion of the green molded body 23 is removed, whereby an unburned dielectric substrate 2a is obtained. Subsequently, through-holes 8 and 9 for through-conductors are formed on the dielectric substrate 2a, and then marginal sections 12 of the opened ends of the through-holes 8 and 9 and internal peripheral surfaces 13 of the holes 8 and 9 are smoothed, by using the eroding step again. Subsequently, a dielectric substrate 2, having a raised section 3 and wing sections 4 and 5 respectively having the through-holes 8 and 9, is obtained by applying a burning step. Thereafter, conductive films are formed on both surfaces of the substrate 2 and, at the same time, through-conductors are formed in the through holes 8 and 9 so as to electrically connect the conductive films formed on both surfaces of the substrate 2 to each other.