The panel includes a plurality of convex portions protruding from a predetermined reference plane, and a plurality of flat portions constituting the reference surface flush, among a plurality of recesses recessed from the reference surface, and the convex portion, the flat and a part or the recess; when provided with the flat portion, the entire periphery of the convex portion each surrounded by the flat portion, and, while the entire periphery of the flat part each surrounded by the convex portion, when provided with the recess, the entire periphery of the convex portion each surrounded by the recess, and, entire periphery of the recess, each surrounded by the convex portion.