In a die assembly (100), plural pairs of extrusion ports (111, 112) are set up on concentric circles different in diameter. The die assembly (100) is also provided with a core material feeding layer (251) which spreads in such a planar state as to be connected to all core material extruding passageways (271a, 272a) and a sheath material feeding layer (181) which spreads in such a planar state as to be connected to all sheath material extruding passageways (141, 142) and the core material and the sheath material are fed through the passageways. This constitution makes it possible to set up extrusion ports (111, 112) in arbitrary positions corresponding to the core material feeding layer (251) and the sheath material feeding layer (181) which each spread in a planar state, which enables simultaneous production of more multilayer extrusions while inhibiting the enlargement of the assembly.