Disclosed is an emulsion binder containing an A-B block copolymer. The A-B block copolymer has a number average molecular weight of 5,000 to 100,000, and a polydispersity index (weight average molecular weight/number average molecular weight) of not greater than 1.7. The polymer block A has an acid value of 0 to 30 mgKOH/g and a glass transition point of not higher than 60°C. The polymer block B has an acid value of 75 to 250 mgKOH/g. The A-B block copolymer has been neutralized with an alkaline material, and has been allowed to self-emulsify in an aqueous medium to form emulsion particles having an average particle size of 30 to 300 nm.