PURPOSE: To improve design of the surface of a metal siding by applying a treatment having a three-dimensional effect to a decorative surface of the metal siding without increasing production cost.

CONSTITUTION: In a manufacturing device for a metal siding comprising a delivery part 4 consisting of an uncoiler 1 and a pinch roller 2, a forming roll part 5 which can form a thin metal plate 3 into a shape so that left and right ends thereof can be engaged with each other in the longitudinal direction, an injection head 7 for feeding raw liquid of plastic foam 6 which will become a core material, and a delivery part 9 of a rear side material 8, a press processing device 10 is disposed between the delivery part 4 and the roll part 5. A die blanking processing is applied to the plate 3 at regular intervals to form notches, and further a press processing device 12 is installed between the roll poart 5 and the head 7. And a vertical joint having inverted U-shape is formed at each notch.