To obtain a copolymer latex that improves pick strength of coated paper and has excellent wet stickiness resistance and depression effect on backing roll stain.

The copolymer latex for coated paper is a copolymer latex obtained by emulsion polymerization of monomers comprising 25-60 mass% of a conjugated diene-based monomer, 1.5-7 mass% of an ethylene unsaturated carboxylic acid monomer composed of a dibasic ethylene-based unsaturated carboxylic acid monomer as an essential component, 10-30 mass% of a vinyl cyanide molecule and 3-63.5 mass% of another copolymerizable monomer by at least two or more stages and has relation between the amount (X) of a carboxylic acid existing on the particle surface of the copolymer latex and the amount (Y) of a carboxylic acid existing in a water phase satisfying formula (1) 0.4<(X)/((X)+(Y))<0.8.