PURPOSE: To prevent the generation of a fire by providing a safe gas supply means for supplying inert gas such as nitrogen gas in order to prevent a fire flame in a painting booth.

CONSTITUTION: Nitrogen gas is supplied into a painting booth 1 through a nitrogen gas pipe 17 under the control of a nitrogen gas supply control unit 15 to hold the concn. of oxygen to a predetermined set value or less. The high voltage from a high voltage generator 12 is supplied to a painting machine 8 through a high voltage cable 11 and the paint from a paint pump 10 is supplied to the painting machine 8 through a paint pipe 9. The paint emitted from the painting machine 8 is finely pulverized by atomizing air due to nitrogen gas and paint particles are deposited to an object 6 which is to be painted along the electrostatic field formed between the painting machine and the object 6 to be painted suspended from a conveyor 5. By this method, the accident such as a fire or explosion in the painting booth can be prevented.