PURPOSE: To paint the surface and reinforce the end part of the building board with the same reverse roll coater by rotating a man roll in the direction reverse to the traveling direction of the building board traveling between the main roll and a backup roll.

CONSTITUTION: The main roll 2 is rotated in the direction reverse to the traveling direction of the building board 5 conveyed between the main roll 2 and the backup roll 4 in the reinforcement of the building board having considerable thickness and made of a frazile material. As a result, a coating material 1 on the peripheral surface of the main roll 2 falls on the surface of the building board 5 to form a coated film 7, and further the coating material 1 is scraped off by the end face 6 of the building board 5 in the conveying direction. Consequently, a coated film 7b is also formed on the end face 6, and the end part of the building board 5 is reinforced by the coated film 7b.