<p>Disclosed is a copper surface treatment agent which can treat a copper surface into a smooth form without requiring an increased number of treatment steps and without requiring any copper surface roughening treatment such as etching, and which enables the adhesion between copper and an insulating material such as a resin to be maintained. The copper surface treatment agent comprises a tin compound and a hydrophilic polymer, wherein the hydrophilic polymer has an epoxy group and a carboxyl group.</p>
