A dielectric line having a sufficient ensured strength and being suitable for mass production and a production method therefor are provided. The production method is a method for manufacturing a dielectric line having a dielectric strip which is provided between two conductive plates approximately parallel to each other and which has a width smaller than that of the conductive plates, and dielectric medium layers which are filled between the conductive plates other than the dielectric strip and which is composed of a porous material having a dielectric constant smaller than that of the dielectric strip. The dielectric line (NRD guide) is produced by film forming steps S11 and S12 in which a film of a dielectric raw material is formed on one of the conductive plates, a strip exposure step S13 in which a part of the above film having a shape corresponding to the dielectric strip is exposed to predetermined light, beams, or vapor, and pore forming steps S15 and S16 in which the entire film of the dielectric raw material is made porous.