PURPOSE: To always effect an uniform flux coating and to prevent the careless dispersion of a flux by controlling by using a shield plate so that a sprayed flux may be coated on a flux liquid tank only at its passing time of a printed circuit board.

CONSTITUTION: When a printed circuit board 7 arrives at the specific position for the upper part opening 16 of a flux liquid tank 11, an initial board detection signal is generated by a positional sensor. A pressurized air is fed to an air pipe 14 and the pressurized air projected from a projection port 15 sprays the flux stuck to a rotary screen 13 like a mist. The mist-like flux is not splashed from the upper opening 16 by being shielded by a mobile shield plate 17 because of its being located at shielding position. At the time when the printed circuit board 7 comes to a fixed regulated position by its moving, a 2nd position detecting signal is generated and the mobile shield plate 17 is rotated to spray a mist-like flux having no density nor turbulent flow from the rotary screen 13. The flux stably splashing from the upper opening 16 is then coated on the necessary processing face of the printed circuit board 7.