A welding device for a non-circular plate, comprising: a chuck for gripping and rotatably supporting a plurality of laminated non-circular plates; and a welding torch for welding outer peripheral edges of adjacent non-circular plates among the plurality of laminated non-circular plates, the welding device being characterized by further comprising: a stationary shield box; a movable shield box which is position-adjustable with respect to the welding torch so as to form a shield space (s) surrounding the welding torch with the stationary shield box; an actuator for enabling position adjustment of the movable shield box with respect to the welding torch; and a control part for controlling an operation of the actuator based on a rotation angle (θ) of the chuck such that an inner surface of the movable shield box approaches the outer peripheral edges of the adjacent non-circular plates in accordance with the rotation angle (θ), wherein the stationary shield box is disposed so as to surround the welding torch, wherein the movable shield box is disposed on an outer side of the stationary shield box relative to the welding torch, and wherein the stationary shield box and the movable shield box are each provided with a shielding gas supply nozzle (54, 56). a chuck for gripping and rotatably supporting a plurality of laminated non-circular plates; and a welding torch for welding outer peripheral edges of adjacent non-circular plates among the plurality of laminated non-circular plates, the welding device being characterized by further comprising: a stationary shield box; a movable shield box which is position-adjustable with respect to the welding torch so as to form a shield space (s) surrounding the welding torch with the stationary shield box; an actuator for enabling position adjustment of the movable shield box with respect to the welding torch; and a control part for controlling an operation of the actuator based on a rotation angle (θ) of the chuck such that an inner surface of the movable shield box approaches the outer peripheral edges of the adjacent non-circular plates in accordance with the rotation angle (θ), wherein the stationary shield box is disposed so as to surround the welding torch, wherein the movable shield box is disposed on an outer side of the stationary shield box relative to the welding torch, and wherein the stationary shield box and the movable shield box are each provided with a shielding gas supply nozzle (54, 56). a stationary shield box; a movable shield box which is position-adjustable with respect to the welding torch so as to form a shield space (s) surrounding the welding torch with the stationary shield box; an actuator for enabling position adjustment of the movable shield box with respect to the welding torch; and a control part for controlling an operation of the actuator based on a rotation angle (θ) of the chuck such that an inner surface of the movable shield box approaches the outer peripheral edges of the adjacent non-circular plates in accordance with the rotation angle (θ), wherein the stationary shield box is disposed so as to surround the welding torch, wherein the movable shield box is disposed on an outer side of the stationary shield box relative to the welding torch, and wherein the stationary shield box and the movable shield box are each provided with a shielding gas supply nozzle (54, 56).