Abstract: An apparatus for treating ascites which is safe and superior in performance and does not cause hemolysis, by removing harmful bacteria or cancer cells contained in ascites, by filtration, concentrating useful proteins, etc. contained therein and returning the resulting concentrate to living body is provided.Said apparatus comprises an ascites-transporting means, a hemolysis-preventive means connected to said ascites-transporting means, a filter for removing bacteria and cancer cells, containing at least one membrane for filtering the ascites which has passed said hemolysis-preventive means, and a concentrating vessel containing at least one membrane for concentrating the ascites thus filtered.