PURPOSE: To perform the change-over operation of inverting inner/outer layer resin in a simple manner and in a short period of time by selectively moving a change-over member to two change-over positions along a longitudinal axis.

CONSTITUTION: In one change-over position 45a, one inclined resin-passage 50 connected to an inner resin communicating passage 22 of a connecting member 20 is formed through an inclined face 43 to which a first extruder 30 is joined, and the other inclined resin-passage 51 connected to an outer resin communicating passage 21 of the connecting member 20 is provided through the other inclined face 44 to which a second extruder 31 is joined. The downstream ends of these inclined resin-passages 50, 51 open to a face 42, and a changer-over passage in the change-over position 45a is constituted of these inclined resin- passages 50, 51. On the other hand, in the other change-over position 45b, one inclined resin-passage 52 connected to the inner resin communicating passage 22 of the connecting member 20 is provided through the inclined face 44, and, furthermore, an inclined resin-passage 53 connected to the outer resin communicating passage 21 is provided through the inclined face 43.