To manufacture large panels efficiently at low cost, and to improve operating efficiency on a construction field.

The large panel consists of a main frame, in which C channels 16, 16 are combined, and an L angle 20 stretched between the mutual C channels 16, 16 of the main frame. Anchors 30 are fixed onto the L angle 20. A steel frame 12 is arranged on the upper side of a molding die 60 so that plates 32 at the front ends of the anchors 30 are disposed into the molding die 60, and the inside of the die 60 is supplied with a premix material for GRC molding. The die is released after curing, glass wool is inserted and charged through a spacer, and a punching metal is installed and the large panel is manufactured.