A molding member is installed and supported on the outer surfaces of supporting members which are mounted on the flange portion of a backdoor of a motor vehicle and the edge portion of a window of the same which are secured to each other. Each supporting member is of E-shape defining first and second spaces therein, in which the flange portion of the backdoor is securely disposed in the first space and the edge portion of the window is securely disposed in the second space.
