In this paper, the results of an experimental study on improvement methods of bending accuracy of 6000 series aluminum alloy hollow square cross-section extruded shapes in press bending are presented. Cross-sectional distortion with buckling is a problem encountered during bending because it reduces the bending accuracy of products. First, a restraining method of buckling by means of an internal mandrel has been examined. Second, some methods of restraining localized deformation by means of a variable dir opening system and counterpressure have been investigated. Experimental results have revealed that the formability of an aluminum alloy cross-sectional shape is improved by restraint buckling and local deformation.