Molding method for producing molded article having a hollow portion

A method for the production of a molded article having a hollow portion by utilizing a gas compression apparatus having a gas source, a compressor composed of a piston and a cylinder, and a discharge valve for controlling the flow of pressurized gas discharged from the cylinder,

• the method including one molding cycle from initiation of injection of a molten resin into a cavity to completion of cooling of the resin in the cavity,
• said one molding cycle including at least two intake-compression steps,
• each of said intake-compression steps comprising an intake step of supplying gas from the gas source to the cylinder and a compression step of compressing and thereby pressurizing the gas by movement of the piston in the cylinder following the intake step and being carried out on the basis of predetermined compressor operation conditions,
• the pressurized gas being introduced through the discharge valve into the molten resin injected into the cavity of a mold, at every intake-compression step in said one molding cycle, thereby forming the hollow portion in the molded article.