According to the present invention, a hollow molded article of high quality can be produced by conducting the following steps of: providing a small-sized molding machine comprising a mold having a pair of mold halves wherein at least one of the mold halves comprises a body and a slidable block; supplying a resin in an unsolidified state between the mold halves to fill a mold cavity having a first clearance with the resin; supplying a pressured 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.