Provided is a shaping device for a roller electrode for seam welding that prepares shapes for a first roller electrode and a second roller electrode attached to an arm of a robot. This shaping device is provided independently from the robot and disposed within rotational range of the arm, and is provided with a first roller and a second roller that are disposed on a line orthogonal to a line joining the rotational centers of the first and second roller electrodes and are in contact with the outer circumferences of the first and second roller electrodes.