A bag connection comprises a first bag, a tube having a blood-drawing needle at the front end, a plurality of second bags, tubes for connecting the first and second bags, and tubes and branch connectors for connecting the second bags to each other. On the other hand, a filter unit includes a filter, and a tube connected at opposite ends thereof to the inlet and outlet of the filter. The tubes of the bag concatenation and the tube of the filter unit have respective markers attached thereto. With these markers used as marks, both tubes are aseptically connected by a tube aseptic connection device, thereby incorporating the filter unit into an intermediate portion of a tube of the bag concatenation.
