A heat radiating plate 10 of a metal material includes a flat plate portion 10a, a large number of columnar protruding portions 10b which protrude from one major surface of the flat plate portion and which are integrated with the flat plate portion, and a reinforcing plate member 12 of a material, which has a higher melting point than that of the flat plate portion and columnar protruding portions and which is arranged in a region, which is arranged in the flat plate portion and which is close to one major surface of the flat plate portion, the reinforcing member passing through the flat plate portion to extend in directions substantially parallel to the one major surface of the flat plate portion and having end faces exposed to the outside, the whole surface of the reinforcing member except for the end faces being bonded directly to the flat plate portion.