PURPOSE: To obtain a good weld zone which is free from welding defect such as blow-holes, etc. by providing an air gap of a suitable interval on a superposed part of a material to be joined, and executing laser welding.

CONSTITUTION: Galvanized steel plates 1, 2 are fixed and held to a working table 15 by a clamper 14, run in the direction vertical to the paper surface and welded by irradiating a laser beam 7. In this case, the galvanized steel plate 1 is brought to plastic working in advance so that an interval G of a gap 13 becomes a prescribed value in a weld zone. Accordingly, the zinc vapor of the galvanized layer escapes from the gap 13. In this way, a pierced hole does not become an irregular shape, a sound shape is held, and as welding advances, the pierced hole can be filled up completely by a molten metal, no blow-hole is formed in a coagulated metal 11, and a good weld zone is obtained.