Abstract: In a method of operating an injection compression molding machine having a stationary metal mold, a movable metal mold, an oil pressure actuator for advancing the movable metal mold toward the stationary metal mold to form a mold cavity therebetween with a predetermined compression clearance .delta. left between the movable and stationary metal molds, a heating cylinder adapted to engage with the stationary metal mold, a hopper for supplying a thermoplastic resin into the heating cylinder, a screw contained in the heating cylinder for injecting molten metal into the mold cavity, an oil pressure motor for rotating the screw and a piston cylinder unit for reciprocating the screw through the heating cylinder, the molten resin is filled in the mold cavity by advancing the screw and the advancement of the movable metal mold is started when the screw reaches a predetermined set position during an injection stroke so as to reduce the compression clearance .delta.