When an absorptive material 1 having a high absorption factor to a laser beam L and a transmissible resin material 2 having a high transmission factor to the laser beam are lapped one upon another and the laser beam is irradiated to the joint portion through the transmissible resin material to fuse the joint portion and to weld both of the resin materials, a laser welding method of the invention disposes a protuberance 5 on the contact side of the absorptive resin material with the transmissible resin material, and irradiates and scans the laser beam along a weld line M while both of the resin materials are kept pressed by using a jig 3 or the like. The sectional shape of the protuberance is a triangle, a rectangle or a trapezoid. Consequently, the invention can improve an initial surface pressure, can reduce a clearance and can provide a weld portion 9 devoid of defects, such as voids, resulting from the entrapment of air.