Agent for treating metal surface, and method for treating metal surface

An agent for treating a metal surface and a method for treating a metal surface are provided with which it is possible to impart excellent electrodeposition coatability (smoothness and throwing power) to a metallic base while heightening the corrosion resistance thereof. The agent for treating a metal surface is for use in a pretreatment of a metallic base in preparation for electrodeposition coating and comprises one or more metallic elements (A) selected from the group consisting of zirconium, titanium, and hafnium, one or more coupling agents (B) selected from the group consisting of silane coupling agents, hydrolyzates thereof, and products of polymerization thereof, and a compound (C) containing a group that undergoes an electrophilic reaction, wherein the compound (C) containing a group that undergoes an electrophilic reaction contains a homocycle and a heterocycle in the molecule and has a solubility in 20oC water of 0.2-30 g/L, and the contents of the metallic elements (A), coupling agents (B), and compound (C) containing a group that undergoes an electrophilic reaction satisfy a given relationship.