A surface treatment solution for autodeposition coating treatment of a metallic material, which is an aqueous solution comprising at least one tannin, at least one crosslinking agent having a crosslinking group capable of thermosetting reaction with a phenolic hydroxyl group and/or a phenolic nucleus, ferric ions, soluble type elemental fluorine, and an oxidizing agent, wherein the solids mass concentration ratio of the tannin to the crosslinking agent is in the range of from 1:1 to 1:10, the molar concentration of the soluble type elemental fluorine is at least 3-fold the molar concentration of the ferric ions, and the pH of the solution is from 2 to 6. The surface treatment solution allows shorter process length as compared with conventional coating processes, generates less environmentally harmful by-products such as sludge, has excellent throwing power at the interior of a pocket structure, does not use environmentally harmful components such as chromium compounds, has corrosion resistance, and allows overcoating of a baking finish on the obtained coating film.