There is provided an injection molding machine provided with an injection mechanism that enables a high-speed injection.The injection molding machine includes: a heating barrel for melting and kneading a resin fed from a hopper, said barrel having an injection nozzle at its front end; a screw movably and rotatably inserted in the heating barrel; a screw drive shaft coupled at its one end to the rear end of the screw; charging means including a charging motor for rotationally driving the screw drive shaft to rotate the screw so as to melt the resin in the heating barrel while conveying the resin forward of the screw, and measure the volume of the molten resin, and torque transmission means for transmitting the driving torque of the charging motor to the screw drive shaft and permitting a displacement of the screw drive shaft in the axial direction; a body frame fixing and supporting the charging motor and the torque transmission means, said frame including a front plate fixing and supporting the base of the heating barrel; injection drive means including a linear-movement shaft coupled to the rear end of the screw drive shaft and movable in the axial direction, and an injection motor for advancing the screw and producing an injection force for injecting the molten resin in the heating barrel; and shaft coupling means for coupling the rear end of the screw drive shaft to the linear-movement shaft such that only a thrust in the axial direction is transmitted to the screw drive shaft.