PURPOSE: To simplify a drive mechanism for respective peripheral wall members by a method wherein a box-form female mold is composed of a plurality of peripheral wall members and a bottom face member, and each of the peripheral wall members is so provided as to be linearly reciprocated between a position where it retracts outward from the bottom face member and a position where it closely abuts against the bottom face member and the other peripheral wall members adjacent thereto to form an original form of the female mold.

CONSTITUTION: In a pair of male and female molds, a double-wall article made of inner and outer walls is produced by clamping a parison supplied between the male and female molds which are separated in proximity to each other. The female mold 10 of a box form is composed of four peripheral. members 12a-12d in two pairs and a bottom face member Each of the peripheral wall members 12a-12d is so provided as to be linearly reciprocated between a position where it retracts outward from the bottom face member and a position where it closely abuts against the bottom face member and the other peripheral wall members adjacent thereto to form an original form of the female mold.