The present invention is a copper film-forming agent containing a copper complex composed of a copper formate and a 5-membered or 6-membered nitrogen-containing heterocyclic compound having from 1 to 3 nitrogen atoms, in which the nitrogen-containing heterocyclic compound has one or two ring structures, the total number of carbon atoms contained in a substituent is from 1 to 5, and an element other than a carbon atom in the compound is not bonded to a hydrogen atom.