The welding chip heats and melts the first welded part and the second welded part, and includes a projected part, a first extension part, and a second extension part. The projected part has a tubular shape with a bottom. One end of the tubular shape extending in a predetermined direction opens and the other end of the tubular shape is closed. The projected part is pushed into the first welded part and the second welded part in the predetermined direction from the opening one end of the tubular shape. The first extension part has a shape extending from a tube outer surface of the projected part and extending annularly around the predetermined direction. The second extension part has a shape extending from the first extension part to the opening one end of the projected part in the predetermined direction and extending annularly around the predetermined direction.