A YAG laser welding is applied to a panel assembly including an outer panel and an inner panel manufactured of, for example, aluminum alloy. The YAG laser welding is conducted by any one of (1) emitting one pulse of a YAG laser onto the panel assembly to laser-weld the panel assembly in the manner of spot welding, (2) providing an outer panel having a slit between portions of the outer panel where weld beads are formed, (3) laser-welding the panel assembly using a first YAG laser having a first laser output and a second YAG laser having a second, lower laser output intermittently along a welding schedule line, and (4) laser-welding the panel assembly on a line of the panel assembly increased in bending rigidity due to a hemming curvature.