PURPOSE: To perform the preheating and welding by a laser beam with the same heating source and to enable the minimum preheating by projecting a laser light on the surface of a board excluding the width of the welding bead part of the board by coating the coating material to absorb the laser light thereon.

CONSTITUTION: The coating material 3 absorbing a laser light is coated on the surface of a board 1, excluding the width of the welding bead part 6 of the surface at welding side of the board 1 in case of performing the laser welding of a sintered alloy tip 2 and the board 1 constituting of a special steel. The board 1 and blade edge tip are preheated with a defocusing beam 4 prior to welding in advance. A just-focusing beam is then projected on the welding bead part 6 where no coating material 3 is coated and the welding is performed. In this way, the hardness reduction due to the temp. up of the board is prevented and the heat resistant strength of the joining part is increased as well in the joining of the board and sintered alloy tip.