In a continuous rolling line wherein the tail end part of a preceding rolled plate and the head end part of a following rolled plate are joined subsequently to a rough rolling and subjected to a following continuous finish rolling: a joining method of rolled plates wherein the tail end of the preceding rolled plate and the head end of the following rolled plate are formed into a nearly rectangular convex and concave shape respectively so as to inlay each other, the convex part and the concave part being combined each other in the same plane as the rolling lines, and then being fed to the continuous finish rolling; a joining method rolled plates wherein the side surface of the parallel inlay is formed in a taper shape in the direction of the plate thickness at any desired location of either the tail end part of the preceding rolled plate or the head end part of the backward rolled plate or of the both parts, and then being fed to the continuous finish rolling; and a joining method of rolled plates wherein the cut parts of the preceding and the following rolled plates are inlaid each other at the same plane, and joining only a part of the side edge of the inlay.