An arc spray gun in which the ends of two metal wires, respectively connected to opposite terminals of a DC power source, are fed to an intersection point to strike and maintain an electric arc, melting the wires. A gas jet directed at the intersection point sprays the molten metal onto the object to be coated. The wire connected to the positive terminal of the power source is of larger diameter than the negative-terminal-connected wire. Parallel guides are provided for feeding the wires through hollow electrodes converging toward the arc-melting zone, the guide path of the larger wire being straighter than that of the smaller wire.