PURPOSE: To improve the environment of molding operation by preventing the scattering of rank odors and gases generated in a molding machine by a method wherein a cover is provided at a place where the fixing base of a mold fastening unit is brought to contact with a screw cylinder and a hose having a dust collector at one end is installed to the cover.

CONSTITUTION: A cover in the form of U 4 is installed to a fixed side plate 3 of a mold fastening unit 2 and the sucking hose 6 of a dust collector 5 is installed to the cover 4. An operating switch 8 of the dust collector 5 is installed to the operating panel 7 of a molding machine. In the dust collector 5, activated charcoal or a filter impregnated with activated charcoal and deodorant is accommodated. When the dust collector 5 is caused to interlock with the purging of molding material, molten molding material is discharged from a screw cylinder 1 under the cover 4 and gases generated from the material temporarily accumulated inside the cover 4, but they are immediately sucked into the sucking hose 6 and they are not scattered around. Upon completion of purging, the dust collector is stopped.