PURPOSE: To improve the transfer property of a cavity surface and the dimensional precision of a molded product by a method in which a parison is molded, a side part blow pin is switched from air to hot water, the parison is filled with hot water and pressed on the surface of a mold, and the hot water is switched to cooling water to cool the parison.

CONSTITUTION: Male and female molds 24, 26 are opened, a parison 22 is hung, the lower part is pinched, low pressure air is introduced from a preblow pin 32, the parison 22 is expanded, and molds are clamped. Blow pins 28, 30 are inserted, high pressure air is injected, and a cavity surface 41 is shaped. Next, hot water is supplied from the blow pin 28 to discharge air from the blow pin 30, the cavity surface 41 is shaped by hot water with which the cavity is filled, and a surface transfer property is improved by the synergistic effect of a heating medium which is passed through a heating pipe. Hot water is switched to cooling water, and the heating medium is switched to a cooling medium, the container of the parison 22 is cooled from the inside and outside to be solidified, and air is introduced from the blow pin 28 to discharge the cooling medium.