According to a laser welding method, an inert gas injection process and welding process are performed. In the inert gas injection process, inert gas is injected into an inside of a first metal pipe; and air inside the first pipe is discharged into the outside. In the welding process, a second metal pipe is irradiated with a laser from radially outward of the second pipe; metal is melted with a penetration depth of a penetration part adjusted such that a leading end of the penetration part is located within thickness of the first pipe; and the first and second pipes are welded together along the circumferential direction to form a pipe joint product. An inner wall of the first pipe maintains its pre-welding metallic luster. An injector includes an injection nozzle, a fuel passage member, a valve member accommodated in the fuel passage member, and a driving unit driving the valve member. The fuel passage member is welded as the first pipe by the laser welding method to maintain pre-welding metallic luster on an inner wall of the fuel passage member.