An injection molding machine comprising: a nozzle which injects a molding material into a mold unit; a flow path opening/closing mechanism which opens or closes a flow path of the molding material in the nozzle; a cylinder having a front end portion in which the nozzle is provided; a screw which is disposed to be rotatable and movable forward or rearward inside the cylinder; a drive source which drives the screw; and a control unit which controls the flow path opening/closing mechanism and the drive source, wherein the flow path opening/closing mechanism includes a valve body which is moved between an open position at which the valve body opens the flow path and a closed position at which the valve body closes the flow path, and a valve body movement mechanism which performs an operation of moving the valve body located at the open position to the closed position to fix the valve body at the closed position and an operation of releasing fixing of the valvebody located at the closedposition to enable a movement of the valve body to the open position by a pressure of the molding material accumulated inside the nozzle, characterized in that the control unit is configured to, after a plasticizing process of accumulating the molding material in a front portion of the cylinder starts and before a filling process of filling an inside of the mold unit with the molding material accumulated in the front portion of the cylinder starts, execute a control of releasing the fixing of the valve body located at the closed position, and after releasing the fixing of the valve body and before starting the filling process, to rotate the screw and/or move the screw forward to increase the pressure of the molding material in front of the screw, and that the control unit is further configured to, after the plasticizing process is completed and before the valve body moves from the closed position to the open position, adjust at least one of a rotation amount and a forward amount of the screw so that the pressure of the molding material in front of the screw is less than a set value. a nozzle which injects a molding material into a mold unit; a flow path opening/closing mechanism which opens or closes a flow path of the molding material in the nozzle; a cylinder having a front end portion in which the nozzle is provided; a screw which is disposed to be rotatable and movable forward or rearward inside the cylinder; a drive source which drives the screw; and a control unit which controls the flow path opening/closing mechanism and the drive source, wherein the flow path opening/closing mechanism includes a valve body which is moved between an open position at which the valve body opens the flow path and a closed position at which the valve body closes the flow path, and a valve body movement mechanism which performs an operation of moving the valve body located at the open position to the closed position to fix the valve body at the closed position and an operation of releasing fixing of the valvebody located at the closedposition to enable a movement of the valve body to the open position by a pressure of the molding material accumulated inside the nozzle, characterized in that the control unit is configured to, after a plasticizing process of accumulating the molding material in a front portion of the cylinder starts and before a filling process of filling an inside of the mold unit with the molding material accumulated in the front portion of the cylinder starts, execute a control of releasing the fixing of the valve body located at the closed position, and after releasing the fixing of the valve body and before starting the filling process, to rotate the screw and/or move the screw forward to increase the pressure of the molding material in front of the screw, and that the control unit is further configured to, after the plasticizing process is completed and before the valve body moves from the closed position to the open position, adjust at least one of a rotation amount and a forward amount of the screw so that the pressure of the molding material in front of the screw is less than a set value.