A welding device for welding outer peripheral edges of overlapping two irregular shaped plates, the device comprising: a rotary table (12a, 12b) to which the overlapping two irregular shaped plates are fixed; a torch unit including a welding torch positioned to face the outer peripheral edges of the two irregular shaped plates fixed to the rotary table; an after-shielding part positioned downstream of the welding torch in a rotational direction of the rotary table (12a, 12b) and disposed on the welding torch, the after-shielding part having a plurality of nozzles (22a, 22b) arranged along the rotational direction and configured to jet a shielding gas to the outer peripheral edges, the plurality of nozzles (22a, 22b) including a first nozzle positioned upstream in the rotational direction and a second nozzle positioned downstream of the first nozzle in the rotational direction; a nozzle actuator disposed on the welding torch and configured to rotationally move the second nozzle in a circumferential direction of the outer peripheral edges; characterized in that the welding device further comprises a controller that has a nozzle posture map in which the orientation of the second nozzle is described by a coordinate, at least for each of regions having different curvatures of the outer peripheral edges, in a two-dimensional coordinate system whose origin is a rotation center of the two irregular shaped plates, and wherein the controller is configured to control the orientation of the second nozzle based on the nozzle posture map, in a direction of decreasing a distance at which the shielding gas jetted from the second nozzle reaches the outer peripheral edges welded by the welding torch. a rotary table (12a, 12b) to which the overlapping two irregular shaped plates are fixed; a torch unit including a welding torch positioned to face the outer peripheral edges of the two irregular shaped plates fixed to the rotary table; an after-shielding part positioned downstream of the welding torch in a rotational direction of the rotary table (12a, 12b) and disposed on the welding torch, the after-shielding part having a plurality of nozzles (22a, 22b) arranged along the rotational direction and configured to jet a shielding gas to the outer peripheral edges, the plurality of nozzles (22a, 22b) including a first nozzle positioned upstream in the rotational direction and a second nozzle positioned downstream of the first nozzle in the rotational direction; a nozzle actuator disposed on the welding torch and configured to rotationally move the second nozzle in a circumferential direction of the outer peripheral edges; characterized in that the welding device further comprises a controller that has a nozzle posture map in which the orientation of the second nozzle is described by a coordinate, at least for each of regions having different curvatures of the outer peripheral edges, in a two-dimensional coordinate system whose origin is a rotation center of the two irregular shaped plates, and wherein the controller is configured to control the orientation of the second nozzle based on the nozzle posture map, in a direction of decreasing a distance at which the shielding gas jetted from the second nozzle reaches the outer peripheral edges welded by the welding torch.