To provide a mixed liquid containing an organocopper compound, having long service life and hard to decompose before a film formation, affording a high film formation rate, efficiently decomposing on a substrate film, to give high volatile products, and capable of giving a copper thin film of high adhesion to the substrate film.

The objective organocopper compound is such that a β-diketone compound and a silyloxy group-bound unsaturated hydrocarbon compound are coordinated to a univalent copper atom and is shown by the formula (1) (wherein, R is an unsaturated hydrocarbon compound-derived group; L is a β-diketone compound-derived group; and X1, X2 and X3 are each H, a 1-5C alkyl or 1-4C alkoxy).