PURPOSE: To form a coating film on only the inner surface of a tubular body, by providing a cathodic body inside a vacuum vessel, evacuating the interior of said vessel, and then introducing reactive gas containing a gaseous metallic compound into it.

CONSTITUTION: A bar-shaped cathodic body 9 is vertically provided inside a vacuum vessel 2 equipped with a gas-supply opening 3 and an exhaust opening 1, in a manner such that it passes through an insulative laminar supporting body 8 provided under a condition electrically isolated from the bottom of the vacuum vessel 2. A tubular substrate 10 to be treated is arranged around the bar-shaped cathodic body 9 as a center, the interior of the vacuum vessel is evacuated, a gaseous metallic compound is introduced therein, DC or AC of 800W2,000V is impressed between the wall of the vacuum vessel and the cathodic body 8, and the substrate to be treated is conjunctly held at a temp. above 500°C. Consequently, ions, neutral particles, etc. formed by the resulting discharge adhere onto the inner surface of the pipe to form the coating film of said metallic compound.