PURPOSE: To flatten a flat plate section and manufacture an insulated panel without warp in foam molding by means of a molding double conveyor by forming a projected line protruding downward and crooking the flat plate sec tion protruding downward.

CONSTITUTION: A plurality of projected line 6 protruding downward for reinforcing or patterning are protruded in parallel with rising edges 2 on a flat plate section 1 of a metal base 3. Then, the whole flat plate section 1 is crooked in a manner that the central section of the flat plate section 1 is protruded downward. Said metal base 3 is fed to a molding double conveyor 4, and foaming resin 5 is foam molded while conveying said metal base. Even if the flat plate section 1 of the metal base 3 is crooked downward, the same is pinched between upper and lower conveyors 9 and 10 of the molding double conveyor 4 and corrected to be flattened by receiving foaming pressure. A resin foamed material 12 composed of foamed and cured foaming resin is backed with the metal base 3. The same is cut into proper sizes to manufacture an insulated panel.