To provide a coating agent usable when bonding mutually metals, mutually polyolefins or the metal to the polyolefin etc., and having excellent storage stability at low temperatures.

The coating agent is produced by dissolving or dispersing a propylene-1-butene random copolymer in an organic solvent. The random copolymer is graft modified with a polar monomer, and comprises a unit derived from propylene in an amount of 60-90 mol%, and a unit derived from 1-butene in an amount of 10-40 mol%. Furthermore, the copolymer has 85% and 97.5% triad isotacticity determined by 13C-NMR spectral measurement, the molecular weight distribution (Mw/Mn) determined by GPC (gel permeation chromatography) within the range of 1-3, 0.1-12 dl/g intrinsic viscosity measured in decalin at 135C, Tm measured by a differential scanning type calorimeter within the range of 40-120C, and the relationship between the Tm and the content M (mol%) of the 1-butene constituent unit satisfying a specific formula.