An injection molding machine comprises a pre-pressure addition means 2 adding a pre-pressure B acting in the opposite direction of a molding material pressure A received by a screw 1 to a detection means 3 and/or the screw 1, the detection means 3 detecting the axial pressures A and B of the screw, and a screw movement control means 4 controlling the axial pressure based on a different between the pre-pressure B and the molding material pressure A, wherein the pre-pressure addition means 2 is made non-contact with the direction means 3, a forward and backward driving motor 17 is disposed adjacent to a heating cylinder 10, and a screw connector 21 at the rear end of the screw 1 is spline-connected inside a rotating rotor of a screw rotating motor 12. According to the machine, the molding material pressure received by the screw can be accurately detected without being affected by the wear of the machine so as to properly control the axial pressure of the screw and to make the machine compact.