A hollow fiber membrane blood purifying device (1) including a cylindrical container (2), a hollow fiber membrane bundle (3), a potting resin fixing portion (4) embedding and fixing the hollow fiber membrane bundle 3 at each end (2a, 2b) of the cylindrical container (2), headers (5) having nozzles (6), and ports (7) further has the structure in which each header (5) and the cylindrical container (2) are welded in at least two regions over the circumference. The inside face of the header (5) is in contact with a potting resin fixing portion cut face (4S) that is formed by cutting an outer side portion of the potting resin fixing portion (4) in the length direction of the cylindrical container (2) than the end face of each end (2a, 2b) of the cylindrical container (2), and the potting resin fixing portion cut face (4S) is in a compressively deformed state.
