This invention provides a copper compound represented by General Formula (I) below. In General Formula (I), R 1 to R 3 independently represent a linear or branched alkyl group with a carbon number of 1 to 5; provided that R 1 and R 2 are a methyl group, R 3 represents a linear or branched alkyl group with a carbon number of 2 to 5; and provided that R 1 is a methyl group and R 2 is an ethyl group, R 3 represents a methyl group or a linear or branched alkyl group with a carbon number of 3 to 5. A starting material for forming a thin film of the present invention includes the copper compound represented by General Formula (I). The present invention can provide a copper compound which has a low melting point, can be conveyed in a liquid state, has a high vapor pressure, and is easily vaporizable, and also a starting material for forming a thin film which uses such a copper compound.