To manufacture a product coil by leveling and trimming cracked parts and defective shape parts in the edge parts of the sheet width, which are generated by multi-pass rolling of a magnesium alloy sheet.

The apparatus includes: a first winding device 11 by which the magnesium alloy coiled material wound around a fixed mandrel can be unwound; a heating furnace 12 which is arranged on the downstream side of the winding machine and heats the magnesium alloy sheet S which is unwound from the coiled material up to a predetermined temperature; a leveler 13 which is arranged on the downstream side of the heating furnace and corrects the defective shape of the magnesium alloy sheet; a trimmer 14 for cutting both side edges of the sheet; and a second winding machine 15 which is arranged on the downstream side of this trimmer 14 and winds the magnesium alloy sheet.