The present invention provides a method for manufacturing a decorative construction plate, the method including subjecting a metal siding material including: a metallic substrate on which a recess-projection pattern having a height difference of 0.5 mm or more is formed and on which an ink receiving layer formed from a resin composition is provided; a core material; and a back-side material, to flame treatment by exposing the metal siding material to flame with an output of 250 kJ/h to 12000 kJ/h per 10-mm width of a flame port of a burner so that the surface temperature of the substrate does not exceed 300° C., followed by performing inkjet printing using an active ray curable ink.