PURPOSE: To make repeating characteristic good and to make setting and switching of injection speed and driving force easy.

CONSTITUTION: A control part 21 receives detecting signals of a driving force sensor 14 and a position sensor 18 and when the actual driving force o a screw becomes larger than the driving force set in a setting part 26, it outputs a signal controlling rotational speed of a motor 6 so as to be the actual driving force equal to a set driving force and when the actual driving force >the set driving force, it outputs a signal controlling the rotational speed of the motor 6 in such a way that the screw 17 is forwarded by the speed set in a setting part 24. A driver part 22 controls the rotational speed of the motor 6 in accordance with a position feedback signal and a speed feedback signal of the position sensor 18 and a control signal of the control part 21.