PURPOSE: To improve the flow and adhesiveness of lacquer by thinly applying oil on a metal surface, such as tin plate, and impressing an alternating voltage between the metal surface and a conductor disposed thereon, thereby generating a corona discharge.

CONSTITUTION: The metal plate 3 is thinly coated with the oil, such as ester based lubricant, and is conveyed to a downstream side via corona regions 19, 20 by means of supply roller pairs 4, 5 and further roller pairs 8 to 15. The metal plate 3 is supported on a supporting bar 21 connected to conductably (groundably) to the apparatus 18 in the corona regions 19, 20 and about 10 kV alternating voltage (15 to 40 kHz) is impressed thereon via a corona electrode group 22 from a high voltage generator. The surface of the metal plate 3 is chemically activated by the ozone evolved by the generation of the corona discharge. At this time, the gaseous ozone is discharged from a fan 29. The metal surface of the metal plate is thus activated and the flow of the lacquer to be applied and the adhesiveness, coatability or the like of the lacquer are improved.