PURPOSE: To correctly detect the extrusion length of a billet from a die by calculating the extrusion length from a die with the moving amt. of a ram and the extrusion ratio in case of extruding a billet in a container with a ram from a die.
CONSTITUTION: A billet B 1 is inputted into a container 21, a stem 27 is advanced by feeding a pressure fluid from a fluid pressure source 41 into the ram extension chamber 26 inside a ram tube 37 and the billet B 1 is extruded as an extrusion material 32 from the die 20 of the container 21 by a dummy 22. The moving amt. of the ram 23 is measured by rotating the encoder 40 of the ram movement detector 36 fitted to the ram 23 by the rack lever 39a fixed to the stem 27. In this case owing to the existence of the gap between the container 21 and billet B 1 and the distance until the dummy 22 abutts the billet B 1 the time when the fluid pressure inside the ram is attained to the pressure conforming to the extrusion start of the billet B 1 is taken as the calculation starting time of the extrusion length on the moving amt. of the ram and the extrusion length of the extrusion material 32 can correctly be calculated.