In the present invention, a conductive film having low resistance is formed on a substrate, said film having excellent storage stability and high dispersion stability as an ink. A copper oxide ink (1) contains a copper oxide (2), a dispersant (3), and a reducing agent. The content of the reducing agent is in the range of formula (1), and the content of the dispersant is in the range of formula (2). (1) 0.00010≤(reducing agent mass/copper oxide mass)≤0.10 (2) 0.0050≤(dispersant mass/copper oxide mass)≤0.30 The reducing agent content promotes the reduction of copper oxide to copper during firing, and promotes the sintering of copper.