A method of production of a chemically treated steel sheet using cathode electrolysis to form a chemically treated coating which stably resupplies Zr ions in a treatment solution and uses an insoluble anode to continuously and stably treat a steel strip by cathode electrolysis in a treatment solution containing Zr ions and fluorine ions, characterized by using two or more types of zirconium compounds selected from predetermined Zr compounds to resupply zirconium ions in a plating solution consumed by the cathode electrolysis during the cathode electrolysis and maintaining a content of ions in the plating solution at zirconium ions: 0.05 to 30 g/liter, fluorine ions: 0.5 to 10 times the content of the zirconium ions, and ions derived from said two or more types of zirconium compounds other than zirconium ions and fluorine ions: not more than 10 times the content of the zirconium ions in performing the cathode electrolysis.