To certainly and uniformly apply oil to the peripheral surface of a metal wire by utilizing static electricity by cyclically changing charge applied to oil mist in charging the oil mist at a time of the application of oil to the peripheral surface of the metal wire by guiding the metal wire through the oil mist.

A nozzle 3 spraying oil is arranged in a treatment tank 2 to supply oil mist 4 to a region where a metal wire 1 passes and a discharge wire 6 is further arranged between the path line of the metal wire 1 and the nozzle 3 and the metal wire 1 is passed through the charged oil mist 4 to be coated with the oil. As an electrode body, a structure formed by providing a plurality of discharge wires 6 between the electrodes 5a and 5b provided to the inside wall of the treatment tank 2 under tension is pref. and voltage is supplied across the electrodes 5a and 5b through a constant voltage device and a pulse generator to cyclically change the charge applied to the oil mist 4. That is, voltage is supplied across the electrodes 5a and 5b in a pulse like state and the charge of the oil mist 4 is cyclically changed.