PURPOSE: To obtain a method of removing residual opaque flux by a method wherein residual opaque flux generated in a printed board soldering process is removed by heating.

CONSTITUTION: The hot air outlet 4 of a hot air blower 1, is made to approach a residual opaque flux 3 on a printed board 2, wherein the hot air outlet 4 is made to approach the residual flux 3 as close as a distance of 5 to 10mm, and a distance between the air outlet, 4 and the opaque flux 3 is adequately controlled on the basis of the temperature and the discharge of hot air of the hot air blower 1. When the residual opaque flux 3 is heated by hot, air jetted out from the hot air outlet 4, the residual opaque flux 3 is melted with time, and hot air is stopped when that, the residual opaque flux disappears is ascertained. Therefore, as residual flux looks opaque when its surface is so roughened as to irregular]y reflect light or it contains air bubbles, the opaque flux residue 2 is heated from outside to melt a flux residual film, whereby the surface of opaque flux residue 2 is flattened and the involved air bubbles are eliminated, so that opaque residual flux can be easily removed.