PROBLEM TO BE SOLVED: To provide an ascites filtration concentrator obtaining a thick protein solution of high protein concentration with no burden on an operator for an additional concentration process or the like without causing a fall in processing speed due to clogging, in a method for concentrating a diluted protein solution to obtain the thick protein solution.SOLUTION: The ascites filtration concentrator 100 includes: a storage container 1 for storing ascites a filtration filter 3 for separating cell components existing in the ascites a first passage 31 connecting the storage container 1 to the filtration filter 3 a polysulfonic hollow fiber membrane type concentration filter 4 given a hydrophilic polymer with predetermined ultrafiltration performance a second passage 32 connecting the filtration filter 3 to the concentration filter 4 a third passage 33 connected to an outlet 3b of the filtration filter 3 a recovery container 2 for recovering the concentrated protein solution a fourth passage 34 connecting a concentrated solution outlet 4b of the concentration filter 4 to the recovery container 2 and a fifth passage 35 connected to a filtrate discharge port 4c of the concentration filter 4.
