This invention provides an automobile water-based paint capable of forming coating film of little metallic mottling and excellent flip-flop property and smoothness, which comprises hydroxyl-containing resin, viscosity-regulating agent and hydrophobic solvent, the viscosity-regulating agent being a copolymer obtained by copolymerizing a monomeric mixture containing a (meth)acrylic acid (salt), monomer represented by the following formula (1)