In order to obtain an injection drive apparatus which is low-priced, can produce a great output torque, and has a satisfactory acceleration/deceleration characteristic, in an injection-molding machine which performs injection by driving a screw by means of servomotors, one or more ball screws (7), used to drive a screw (2) in the axial direction, are driven by means of a plurality of servomotors (M1, M2), a position detector (P1) for detecting the screw position is provided only for one servomotor (M1), and the servomotors (M1, M2) are provided individually with power amplifiers, which are controlled by means of one control circuit so that the individual servomotors (M1, M2) are controlled in synchronism with one another.