Provided is an injection molding machine whereby drive can be reliably transmitted to a ball screw shaft driven during execution of an injection step. An injection molding machine provided with: a ball screw mechanism (10) comprising a ball screw shaft (8) provided so as to be able to rotate, and a nut body (9) screwed onto the ball screw shaft; a bearing (12) for supporting the ball screw shaft (8); and a pusher plate (7) to which the bearing (12) is mounted, the pusher plate (7) being able to advance and retreat, and the pusher plate (7) being advanced in conjunction with the rotation of the ball screw shaft (8) when an injection step is performed; there being provided: a cylindrical sleeve (13) fitted on an external periphery of the ball screw shaft (8) and disposed between the ball screw shaft (8) and the bearing (12); a lock nut (14) for preventing the sleeve (13) fitted on the external periphery of the ball screw shaft (8) from coming off, the lock nut (14) being screwed onto the ball screw shaft (8); and a pulley (15) mounted to the sleeve (13).