To provide a resin composition for a primer coating having corrosion resistance, chemical resistance, processability, adhesiveness, etc., comparable or superior to the case of using a chromium-based rustproofing agent even by using a non-chromium rustproofing agent and to provide a coated metal plate produced by laminating and curing the resin composition.

The resin composition for coating contains (A) an aromatic polyester resin having a number-average molecular weight of 10,000 and (B) a hyper-branch polymer, provided that the hydroxyl value of the composition is 25 KOHmg/g and 120 KOHmg/g based on the total weight of the components (A) and (B). The invention further provides a coated metal plate coated with the coating composition.