PURPOSE: To cast gratings having various irregular designs, by providing one set of fixing molds and movable molds to a die-cast machine, and installing core molds various engravings are given, to the fixing mold allowable to mount and demount.

CONSTITUTION: To an aluminum die-cast machine M of gratings for a drainage hole for paved road, a gutter, and the like, one set of fixing molds 2 corresponding to the front surface of the grating, and movable molds 1 corresponding to the front surface of the grating, are provided. And plural sorts of core molds 3 which can be installed to the movable mold 1 and have various irregular designs of engravings are prepared. And a core mold 3 having a desired irregular design is installed to the movable mold 1, and aluminum grating is casted by using the die-cast machine M being controlled automatically through an automatic control device. Consequently, gratings with various designs can be manufactured by converting the core mold in various ways.