To provide a welded structure manufacturing method that can manufacture a welded structure welded firmly with a first member and a second member.

When a first outer face 31 is assembled flush with a second outer face 41, a case body member 30 (first member) and a cap member 40 (second member) before welding includes a projecting part 25 which is at least either a first projecting part 35 that projects from the first outer face 31 or a second projecting part 45 that projects from the second outer face 41. The projecting part 25 is positioned between the first outer face 31 and the second outer face 41. With respect to the case body member 30 and the cap member 40 before welding, a laser beam LB (energy beam) is irradiated to the projecting part 25 to weld the case body member 30 with the cap member 40 as the projecting part 25 being a part of welded part 52 in a state that the first outer face 31 is flush with the second outer face 41, and the projecting part 25 is arranged between the first outer face 31 and the second outer face 41.