PURPOSE: To sufficiently clean even the fine corners of a printed circuit board by immersing a material to be cleaned into water, immersing the material pulled up from the water into a solvent mixture composed of water and an org. solvent compatible with water, pulling up the material therefrom and immersing the material into the org. solvent compatible with water.

CONSTITUTION: The material to be cleaned, such as printed circuit board, is immersed into the water, such as pure water, in a tank 1. The material pulled up from the water is immersed into the solvent mixture composed of 100 pts.wt. water and 40 to 200 pts.wt. org. solvent compatible with water (e.g. methanol) in a tank 2. The material pulled up from the solvent mixture is immersed into the org. solvent compatible with water (e.g. methanol) in a tank 3. As a result, the sufficient cleaning of even the fine corners of the printed circuit board is possible and the flux sticking to the fine corners is removed.