apparatus for making corner joints of sealing plastic profiles , or moldings , for windows , doors or the like , including a base plate on which two profile holding means , each having a bottom formed with a groove for accommodating the continuous profile to be held and a pivotable lid for covering or opening the accommodating groove are mounted , one fixedly and one pivotally . a welding means pivotable relative to the holding means , is provided which cuts the miter with the holding means in line and heats the cut edges . the pivotal holding means is moved toward the fixed one and the cut and heated edges of the profile are welded together .