PURPOSE: To improve strength by covering a board with a glass cloth coated with synthetic resin and surrounding the outer peripheral part of the glass cloth with the first pipe member and arranging the second pipe member along the surface and covering the pipe member with a sheet and making the whole pipe member into vacuum.

CONSTITUTION: A board 10 is covered with a glass cloth 13 coated with synthetic resin. The board 10 is placed on a vinyl sheet 21, and the first annular pipe member 22 is installed so as to surround the board 10. A suction pipe 23 is connected at a proper position on the pipe member 22. The second pipe members 31-33 made of Cloth are installed inside the first pipe member 22, and connected with the pipe member 22. Covering by the upper side sheet is performed, and after the upper and lower sheets 21 are sealed with a sealing member 41 on the outer peripheral part of the annular pipe member 22, the sealed pipe members 22, 31-33 are made vacuum, and the air on the whole surface of the board 10 is removed from the cloth. Therefore, the glass cloth covering the board 10 is uniformly pressed, and the synthetic resin is allowed to permeate sufficiently, and strength can be improved.