An arm of a coating robot is used to prevent external leakage of a high voltage. A tank 25 is installed on a robotic arm 1 and contains water as an actuating liquid. The water is supplied to a paint cartridge 4 by a pump 24 controlled by a controller 40. The water sent from the pump 24 under pressure is supplied to the paint cartridge 4 by a conduit tube 12. A high voltage generator 45 and a bleeder resistor 46 are combined with the tank 25 such that a high voltage generated by the high voltage generator 45 is supplied to the electrostatic paint applicator 2 via the water. For replenishment of water to the tank 25 is attained by relatively connecting a nozzle 32 in communication with a water source 34 to a main pipe 23. While the high voltage generator 45 generates a high voltage, the nozzle 32 and the main pipe 23 are kept disconnected to maintain electrical insulation between the nozzle 32 and the main pipe 23.
