To provide a chemical conversion treatment method for metal capable of easily maintaining and controlling the concentration of effective components to the prescribed one.

The chemical conversion treatment method for metal is performed by a chemical conversion treatment system composed of a chemical conversion treatment reaction means comprising: a line provided with a work count means installed in such a manner that a carrying means of continuously carrying two or more kinds of works to each treatment means in order and the works can be counted so as to be distinguished, respectively; a chemical conversion tank filled with a chemical conversion reaction treatment solution; a replenishment tank connected with the chemical conversion tank via a replenishment flow passage and filled with a chemical conversion reaction treatment solution for replenishment; an exhaust flow passage for exhausting the solution from the chemical conversion tank; a replenishing amount control means provided at the replenishment flow passage; and an exhausting amount control means provided at the exhaust flow passage. In the chemical conversion reaction treatment solution, by the control of the replenishing amount control means and the exhausting amount control means based on the number of counts obtained by the work count means, the replenishing amount of the chemical conversion reaction treatment solution for replenishment and the exhausting amount of the chemical conversion reaction treatment solution in the chemical conversion tank are controlled, and the concentration of effective components in the chemical conversion reaction treatment solution is controlled.