Process for producing hollow resin molded article

A process for producing a hollow molded article comprising:

• supplying a resin in an unsolidified state between a first mold surface and second mold surface to a mold to fill a cavity with the resin, wherein the mold includes a first mold half and a second mold half, the first mold half has a first mold surface, the second mold half has a second mold surface, the mold surfaces together define the cavity, at least one of the mold halves can move so that the mold surfaces approach and go away from each other, at least one of the mold halves comprises a body and a slidable block, the mold surface of the mold half comprising the body and the slidable block comprises a surface of the body and a surface of the slidable block, the slidable block can move from a first position to a second position, the movement of the slidable block from the first position to the second position expands the cavity, the surface of the slidable block being at a greater distance from the other mold half surface than the surface of the body, and the cavity has a first clearance;
• supplying a pressurized fluid into the resin lying between the mold surfaces:
• moving the slidable block from a first position to a second position;
• opening the mold until a cavity clearance becomes a second clearance which is larger than the first clearance;
• and
• opening the mold to take out the hollow molded article.