A coating film is formed on a surface of a coating object by adhering a coating powder to the coating object by spraying the coating powder from an electrostatic gun together with a compressed gas. A voltage not smaller than 80 kV but not larger than 100 kV is applied between the electrostatic gun and the coating object. Moreover, a current flowed between the electrostatic gun and the coating object is set to be not smaller than 10 μA but not larger than 20 μA. Further, a pressure of the compressed gas for spraying the coating powder is set to be not smaller than 3 kgf/cm2 but not larger than 6 kgf/cm2.