PURPOSE: To absorb decompression without changing an external shape regardless of the magnitude of the volume of deformation by decompression in a vessel by forming the title preform of a solid mouth section and a drum section and a bottom formed of a hollow wall composed of an inside layer and an outside layer while holding a hollow layer and forming a small-diametral opening-shaped gate section at the lower end of the outside layer of the bottom.

CONSTITUTION: A preform called the so-called parison has a solid mouth section 1 and a drum section 2 and a bottom 3 formed of a hollow wall 20 consisting of an inside layer 22 and an outside layer 23 while holding a hollow layer 21. A central section 31 as a section pushed by an orientation rod at the time of biaxially-oriented blow molding is shaped to the inside layer 22 of the bottom 3, a gate section 40 is formed to the outside layer 23 of the bottom 3, and the gate section 40 has a small-diametral hole section 41 communicated with the hollow layer 21. The preform can be molded through a G.I.P molding method (Gas Injection Process, Mannesmsann Demag Ltd.) an A.M.P molding method (an Air Mold Process, Battenfeld Ltd.) or the like.