PURPOSE: To shorten the changing time of a die stack by arranging a pusher ring for positioning a planer-type part so as to be possible to advance/retreat to a platen of the die stack by hanging a cylinder rod to shift the die stack in the reverse extrusion direction by using the pusher ring at the waiting position for changing.

CONSTITUTION: The die stack. 24 is laid on a die cassette 25 through an automatic charging device. Successively, the die stacks 24A, 24B are pushed to the die cassette 25A, 25B by extending the pusher rings in the reverse extrusion direction while retreating a die changer tray 74 to the front and the rear parts so as to be possible to advance/retreat from the planer-type window formed at the standing-up wall surface of the die cassette 25 by engaging with the rod of a cylinder 78 arranged on the die changer tray 74. Thereafter, a die slide 22 is shifted in the width direction of the machine by working a cylinder 78 engaged with the die slide 22 so as to execute the extrusion of a billet at the press center and then, the idle time is shortened.