PLATE-LIKE BODY

Provided is a plate-like body capable of ensuring its sufficient rigidity without increasing the thickness thereof. Plural convex portions 2 are formed on an aluminum flat plate through embossing processing so that a flat plate portion between the convex portions 2 does not remain in a linear shape. Each one of the convex portions is formed in a hexagonal shape in a plan view, and has a longitudinal section thereof, which includes vertices forming opposing corners of the hexagonal shape, in a circular arc shape. Then, the optimal value of the convex height H to the convex width W1 is about 16.3% above which the performance improvement rate starts to gradually decrease. However, it is thought that the appropriate range of the convex height H to the convex width W1 is the range of from 12% to 20.0% when taking the satisfactory performance improvement rate into consideration.