To prevent poor quality of weld in a welding process for a thick material or for welding a gap, the laser welding apparatus has granular flux (3) supplied to a side of the base material (W) opposite to the side where a laser beam is directed and a pressing member (5) that presses the granular flux onto the base material (W) upon receiving fluid therein. Either the flux prevents the laser beam that coming through the base material (W) from penetrating the flux or the thickness of molten flux is selected so that the laser beam coming through the base material (W) does not penetrate the molten flux.