Provided is a hollow-fiber membrane module including: a cylindrical casing having a treating-liquid inlet port and a treating-liquid outlet port a hollow-fiber membrane bundle mounted within the cylindrical casing while being aligned in one direction potting layers fixing both ends of the hollow-fiber membrane bundle to an inner wall of the cylindrical casing such that hollow sections of hollow-fiber membranes are open and header members surrounding opened end surfaces of the hollow-fiber membrane bundle, the header members being attached to respective ends of the cylindrical casing and having a treated-liquid inlet port and a treated-liquid outlet port, wherein the hollow-fiber membrane module further includes an upper baffle plate provided in the cylindrical casing at a position immediately below the treating-liquid inlet port with a predetermined gap from the inner opening of the treating-liquid inlet port of the cylindrical casing, and a lower baffle plate provided at a position at which the lower baffle plate is line symmetric to the upper baffle plate with respect to an axis of the casing, and no baffle plate is present on an inner circumference of the cylindrical casing between the upper baffle plate and the lower baffle plate. Consequently, the flow speed of the treating liquid can be made more uniform, and the hollow-fiber membrane module can be adopted industrially.
