PURPOSE: To control partial thickness in the circumferential direction of a desired parison accurately and easily by oppositely disposing a fixed side roller and a moved side roller centering around a parison.

CONSTITUTION: When a resin fed into a resin flow path 32 is pushed by an extrusion plunger 7 and extruded and operated from a nozzle slit 5, axial thickness setting from an axial thickness setter 37 corresponding to the position of the extrusion plunger 7 detected by the positional detector 35 of the extrusion plunger is output, a parison control cylinder 9 is moved, and a mandrel 3 is moved vertically, thus controlling thickness in the axial direction of a parison 4. A cylinder 26 is shifted vertically, and moved at the synchronous speed of the vertical shifting of the mandrel 3, and both shafts of a fixed side roller 10 and a moved side roller 20 are controlled so as to be positioned on the same plane. A traverse cylinder 27 controls thickness in the circumferential direction of the parison 4 hung down from the nozzle slit 5 by changing the space of the fixed side roller 10 and the moved side roller 20.