Abstract: In a coating film forming method in which the thermosetting water-borne color paint (A) is coated on the surface of the substrate, then a thermosetting water-borne paint containing color pigment and/or glittering pigment (B) is coated on said coated surf ace, and, after preheating as necessary, a thermosetting clear paint (C) is coated and after that said 3-layer coating films of (A), (B) and (C) are simultaneously cured by heating, an accelerator to thicken is atomized on the coated surface of a thermosetting water-borne color paint (A), when said paint is coated or after said paint is coated.