PURPOSE: To prevent the generation of defects in shape of an extruded material by providing a shape constraining mechanism by which the cross-sectional shape of the extruded material is constrained into a proper shape near by the forming gap of a die and in front in the extruding direction.

CONSTITUTION: A billet B is charged in a container 2 and a stem is forward driven. The billet B is passed through the forming gap 15 of the die 7 and the extruded material E having a prescribed cross section is extruded. In the case that unwilling deformation is generated in the shape of the cross-sectional face of the extruded material E which comes out of the forming gap 15 of die, the extruded material is subjected to shape constraining action by a shape constraining mechanism 5. Then, the extruded material E is entered into a shape constraining member 18 after a relief hole 16 of die, held and corrected so that the shape of the cross-sectional face is proper. The shape constraining member 18 is provided on a backer 9 which is situated just after the die 7, so correction of the extruded material E by shape constraint is effectively executed. The extruded material E excellent in shape accuracy is stably extruded.