PURPOSE: To restrain the metal flow from the outer peripheral part to the center part at the rear end part of a billet and to prevent the blister in a die material by removing the air between an extrusion container and the billet till the time before starting the extrusion from a gap between the end surface of the die and the side end surface of the die of the container mutually brought into no contact with each other.

CONSTITUTION: The billet 13 cooling the rear end part thereof to a desired temp. is pushed with an extrusion stem 14 to push the billet 13 against the die 3, and then, the billet 13 is squeezed and the air between the container 1 and the billet 13 is compressed. This compressed air must be sucked and removed from the front end of the container 1 before extruding the billet 13 from the die. At this time, the sealing is executed with a seal block 40 arranged to the end surface of the container at the stem 14 side so as to be freely opened/ closed in the axial direction of the container 1. Successively, the interval between a sealing being freely shifted in the axial direction by engaging an outer ring 10 fitted to the tip part of the container and the end surface at the container side, is sealed to suck the air.