PURPOSE: To enable to perform efficient injection work, by providing a filter in a vent hole, in an inline screw type injection molding machine which is constituted by a method wherein a screw is inserted into a heating cylinder.

CONSTITUTION: Gas in molten resin in a heating cylinder is sucked by vacuum pressure to be acted upon the gas through a gap 6 of the inside of a suction cover 5 and a filter 4 of the inside of a vent hole 3 from a vacuum pump P and gets out to a pump P side, through which the resin M is deaerated. In this instance, it does not happen that the resin M flows in the inside of the vent hole 3 as the passing of the resin M is interrupted by the filter 4. Cleaning work, therefore, of the vent hole and the circumference of the same becomes unnecessary and it does not happen that the residual resin is mixed with the molten resin at the time of change of the resin.