a method and apparatus for forming a thermoplastic resin vessel including a bottom plate and at least two side plates is provided . the bottom plate or portion is applied to the surface of an inner mold by advancing a bottom mold carrying the bottom plate . the side plates or portions are formed along a concave surface of side molds and is then positioned around the inner mold to completely surround the inner mold to form a tube which holds the bottom plate therein . the outer mold is then removed and the vessel formed by the tube and bottom plate is then removed from the inner mold .