Concentrate dilute protein solutions such as ascites to obtain a concentrated protein solution, without reducing the concentration efficiency due to clogging, and obtaining a concentrated protein solution with a high protein concentration without additional processing time such as an additional concentration step An object of the present invention is to provide a method for producing a highly concentrated protein solution. The present invention relates to a polysulfone-based hollow fiber membrane type in which a low-concentration protein solution is passed through a circuit from a storage container in which the low-concentration protein solution is stored, and an ultrafiltration performance is 85 mL to 150 mL / min / 200 mmHg and a hydrophilic polymer is added. The first step of allowing the ascites concentration filter to pass through and sending the filtrate from the filtration side outlet of the filter, and sending the high concentration protein solution from the filter outlet, and the high concentration protein solution sent from the filter outlet A first step of passing the low concentration protein solution through the ascites concentration filter at a first flow rate, and a second step of recovering the low concentration protein solution. When a predetermined amount or more is delivered from the total amount, the low-concentration protein solution is passed through the ascites concentration filter at a second flow rate that is faster than the first flow rate. Comprising a second step, the a process for producing a high concentration protein solution. [Selection] Figure 1腹水などの希薄なタンパク質溶液を濃縮し、濃厚なタンパク質溶液を得る方法において、目詰まりによる濃縮効率低下をきたさず、追加濃縮工程などの処理時間の追加なしで高いタンパク質濃度の濃厚タンパク質溶液を得ることができる、高濃度タンパク質溶液の製造方法を提供することを目的とする。本発明は、低濃度タンパク質溶液を貯留した貯留容器から回路を通じて低濃度タンパク質溶液を、限外濾過性能が８５ｍＬ～１５０ｍＬ／分／２００ｍｍＨｇであり親水性高分子が付与されたポリスルホン系中空糸膜型の腹水濃縮用フィルタに通液させ、フィルタの濾過側出口から濾液を送出させるとともに、フィルタの出口から高濃度タンパク質溶液を送出させる第１の工程と、フィルタの出口から送出された高濃度タンパク質溶液を回収容器に回収する第２の工程と、を含み、第１の工程が、低濃度タンパク質溶液を第１の流速で腹水濃縮用フィルタに通液させる第１のステ
