Abstract: A method of roll forming hollow parts comprises introducing a workpiece into the space between a plurality of rolls rotatably arranged in spaced and parallel relationship, in parallel with the axes of the rolls, imparting rotation to the workpiece from drives through either the rolls or flanges disposed at both ends of the workpiece, at the same time forcing mandrels, slidably fitted at ends in the central openings of the flanges, through the openings into the workpiece, longitudinally from the both ends thereof, toward each other, and removing the excess metal left in the midportion of the workpiece between the mandrels by slightly moving the rolls toward each other for added compression, thereby producing spaces between the mandrels and the workpiece, and by moving the mandrels axially together with the excess metal to separate the latter from the rest of the workpiece.