PURPOSE: To prevent the contamination of plastic containers by mandrel, etc., by covering the tip and periphery of blow and injection mandrels to be vertically moved and also the upper opening and its neighbor of molds with the atmosphere of aseptic air in a plastic container molding machine.

CONSTITUTION: Aseptic pressure air is supplied from an air supply and discharge port, and a parison 6 is expanded along a die 8 and molded into a container 14 by blow molding. An injection mandrel 18 is then slightly lowered, the valve of the tip is opened, and a packing material is injected into the container 14. A blow and injection mandrel 11 is then raised, and the opening of the container 14 is closed by a closer 19. During the period, aseptic pressure air to be jetted from a germ-free chamber 12 is sent to the peripheral area of the mandrel 11 and the space between the mold device 3 and the germ-free chamber 12 and the intrusion of the open air is prevented. The contamination of the parison 6 and the container 14 by pollutants from the open air can thus be prevented. A through process of the molding machine under aseptic condition is performed in this way.