PURPOSE: To enable a leveling solder coater device to carry out a leveling operation even if a printed wiring board varies in thickness by a method wherein metal leveling rollers are provided coming into contact with an oxidation preventing oil surface.

CONSTITUTION: A clamped printed wiring board 8 is made to descend downward as guided by guide rollers 7 and dipped into a molten solder passing between leveling rollers 5 controlled in roller space corresponding to the thickness of the printed wiring board 8. Then, the printed wiring board 8 coated with a molten solder layer is made to pass through an oil film 3 surface as pulled up. The oil film formed on the leveling rollers 5 is successively transferred to the solder layer formed on the printed wiring board 8 as the rollers 5 rotate. At the same time, the solder layer formed on the wiring board 8 is set constant in thickness. Furthermore, an air knife is turned ON, air of high temperature and high pressure is blown against both the sides of the printed wiring board 8 not only to level the solder layer but also to remove excessive solder.