PURPOSE: To improve the charging and discharging efficiency of a billet and to use effectively the space in a furnace, by computing and storing the order, number and lengths of billets in the furnace and the length of the next charging billet, and charging and discharging the billets by a computed length of stroke, at the time when a discharge command is outputted from an extruder.

CONSTITUTION: The order of lines, order in each line, number and lengths of billets 10, in a heating furnace 1, and the length of the next charging billet, are computed and stored in a computer. By an extrusion-command signal from an extruder, the billet is discharged or charged and discharged by a computed stroke, in prescribed order and based on said storage, with the aid of a stroking machine 7. Thus, the efficiency of charging and discharging the billet is enhanced, and the space in the heating furnace 1 is effectively utilized.