The present invention provides a method for manufacturing a wall panel for which extremely precise external dimensions can be attained.　This manufacturing method comprises: a step B1 in which a plate material (10) to which a sheet (39) has been attached is prepared, and a notch part that includes a first reference line (21) is formed in a first corner section (11); a step B2 in which a notch part that includes a second reference line (22) is formed in the first corner section (11); a step B3 in which a notch part that includes a third reference line (23) is formed in a second corner section (12); a step C1 in which the second reference line (22) is abutted and bent at a prescribed location to form a first bent surface (31b); a step C2 in which the first bent surface (31b) is abutted and bent at a prescribed location to form a second bent surface (32b); a step E1 in which the first reference line (21) and the third reference line (23) are abutted and bent at a prescribe location to form a third bent surface (34c); and a step E2 in which the third bend surface (34c) is abutted and bent at a prescribed location to form a fourth bent surface (33c).