PURPOSE: To improve the texture of appearance by printing a color membrane with a high polymer thin film, sending it into a water tank horizontally, covering a recording tape outer case surface with the color membrane flatly using a hydraulic principle, and a spraying transparent paint onto the outer case surface for forming a protective film.

CONSTITUTION: After giving cleaning, dust removal, and static eliminating process to the surface of a recording tape outer case 40, a color membrane is printed on the recording tape outer case 40 with a high polymer thin film of a polyhydric alcohol hardening type polyurethane. When the outer shell 40 is fed into a water tank horizontally and the color membrane is applied onto the outer case surface utilizing a hydraulic principle, the color membrane on a remaining part is melted automatically. The recording tape outer case 40 after the treatment is fed into the other water tank for cleaning. After conducting bake drying work, a protective film is formed by spraying a synthetic resin, cellulose, rubber derivatives or the like onto the surface of the outer case 40. After drying, a magnetic tape is wound by combining its part with an accessory to finish a product.