A filter unit (14) comprises an inlet (151) and an outlet (152), a filter medium (15) to remove specific components from fluid introduced through said inlet (151), and a tube (16). Both ends of the tube (16) are connected to said inlet (151) and said outlet (152). The filter unit (14) is adapted to be put to use by cutting said tube (16) midway and aseptically connecting the cut tube (16) to another tube (5, 13).