The velocity distrubution at the exit of extrusion die depends on the width of bearing land very much. When uniform bearing land without flow guide is used, the material which is extended through the same die does not, deflect to the constant direction, but when the flow guide is equipped and then the volume compensation is done accurately, the material deflects to one constant direction. Therfore, the part of problem can be known exactly, and extrusion products of straight shape can be produced by the corrected bearing land width.