There is provided a rolled plate joining apparatus equipped with a truck that can travel reversibly in the rolling direction, tailing end pinch rolls that are mounted on the truck and can be moved vertically with the tailing end of a preceding rolled plate pinched horizontally, leading end pinch rolls that are mounted on the truck and can pinch horizontally the leading end of a succeeding rolled plate, machining apparatuses for cutting one surface of the tailing end of the preceding rolled plate and the other surface of the leading end of the succeeding rolled plate, and a pressure welding apparatus for compressing the preceding rolled plate and the succeeding rolled plate with the machined surfaces of the preceding rolled plate and the succeeding rolled plate overlapped to reduce them approximately to the thickness of the rolled plates, including a tailing end centering apparatus placed between the tailing end pinch rolls and the pressure welding apparatus for pressing the opposite width ends of the tailing end of the rolled plate to align the center line of the rolled plate with the center line of the joining apparatus in the rolling direction and a leading end centering apparatus placed between the pressure welding apparatus and the leading end pinch rolls for pressing the opposite width ends of the leading end of the rolled plate to align the center line of the rolled plate with the center line of the joining apparatus in the rolling direction.