A current sensor for detecting a full return current is connected to a high voltage generator. A leakage current detector including current sensors for detecting a leakage current is provided at the surface of the cover of a coating machine, air passages and a paint passage. Based on current detection values obtained by the current sensors, a high voltage control unit controls a power supply voltage control unit and a high voltage to be output from the high voltage generator can be raised or dropped. By employing the current detection values, the high voltage control unit can identify and provide notification of a location where the leakage current is increased and the insulation is deteriorated, and can request an operator to perform maintenance for the pertinent location. Further, upon occurrence of the insulation being deteriorated, the high voltage control unit can stop the high voltage supply.