Abstract: An objective of the present invention is to provide a cylindrical, continuous plasma-processing apparatus capable of modifying the surface of a longitudinal substrate by a plasma process without the use of a vacuum, which has been required in the prior art.The cylindrical, continuous plasma-processing apparatus is comprised of, as a major portion, a hollow cylinder formed of a porous outer periphery wall made of ceramics, rubbers, or glass, a porous network electrode, and a dielectric inner periphery wall. The interior of this cylinder portion contains a metallic pipe whose surface is covered by a dielectric wall such that when a gas is introduced therein, the gas can be diffused into the cylinder portion through perforations. In a space between the cylinder portion and the metallic pipe, there is an antenna, the surface of which is covered by a dielectric.