PURPOSE: To improve smoothness of the vertical surface of an object to be painted, by blowing air in setting process of bilayered coatings formed on the object wet-on-wet painting of liquid paints.

CONSTITUTION: An object to be painted is coated with bilayered coatings by wet-on-wet painting of liquid paints. After the painting, air is blown to the vertical surface of the object at 1W50m/sec blowing speed in a setting period before baking, so that sag and crimp of paint may be suppressed. Then, the bilayered coatings are simultaneously cured to form a 2-coat-1-base coating. Thus, the vertical surface of the object is made smooth excellently by blowing air in setting process.