PURPOSE: To realize an optimum roll bond panel for the positive utilization of radiant heat by anodically oxidizing an Al alloy plate which is specifically composed and specifically controlled.

CONSTITUTION: Two metal plates 1, 2 are adhered by pressure by interposing a press-adhere preventive agent 3 between the plates, a fluid pressure is introduced to non press-adhere parts to expand the metal plates 1, 2, and voids 5 are formed. A metal plate is used an Al-Mn based Al alloy rolled sheet containing 0.3-4.3wt.% Mn, the balance Al and inevitable impurities, and dispersing the deposit of Al-Mn based intermetallic compound and having 0.01-3μm grain size. Also, at least on one side of the surface of the roll bond panel, an anodically oxidized film with a thickness a thickness of 10μm or more is formed.