PURPOSE: To remove graphite banks in the corners of a square bulb and obtain an uniform coat by preliminarily spraying an oily resin on the outer surface of a cathode-ray tube bulb requiring no conductivity followed by drying, and dipping it in a graphite suspension with its funnel part down.

CONSTITUTION: A cover 1 of solvent-resistant plate is fitted to a funnel opening part, and an oily resin and an acrylic resin solution are sprayed from the bulb outer surface and upper part followed by drying to form a first coat 2 only on the outer surface. Then, the bulb is dipped in a graphite suspension 4 with a funnel part 5 down up to the part squiring a graphite coat as a conductive film to form a graphite coat 3 which is a second coat. When the bulb is pulled up, the graphite coat 3 is formed only on the inner surface. Burning is conducted to decompose the acrylic resin, whereby the first coat 2 on the outer surface is completely removed.