A hollow fiber membrane module comprising: an introduction case comprising a housing formed, at one side thereof, with a fluid inlet, a plurality of accommodation spaces (112, 114) formed in the housing in a vertically stacked state such that a gap is defined between adjacent ones of the accommodation spaces (112, 114), a first channel formed between an uppermost one of the accommodation spaces (112, 114) and the housing, a second channel formed between a lowermost one of the accommodation spaces (112, 114) and the housing, and an intermediate channel formed at the gap, the first, second, and intermediate channels communicating with the fluid inlet; a discharge case spaced apart from the introduction case in a horizontal direction, the discharge case comprising a plurality of accommodation spaces (312, 314) defined in the discharge case, and a fluid outlet formed at one side of the discharge case; a connecting case arranged between the discharge case and the introduction case, a plurality of hollow fiber bundles extending through the accommodation spaces (112, 114) of the introduction case, an interior of the connecting case, and the accommodation spaces (312, 314) of the discharge case, to be accommodated therein; and barrier walls arranged to enclose the accommodation spaces (112, 114) such that the accommodation spaces (112, 114) are defined by the barrier walls, respectively, wherein a plurality of first introduction windows, a plurality of second introduction windows, and a plurality of intermediate windows to communicate the first, second, and intermediate channels (143, 144, 145) are formed at the barrier walls, to be arranged in a width direction of the barrier walls, wherein cross-sectional areas of the first and second channels (143, 144) are smaller than a cross-sectional area of the intermediate channel, wherein each of the first and second channels (143, 144) has a cross-sectional area gradually reduced in a direction from a channel end toward the fluid inlet to an opposite channel end. an introduction case comprising a housing formed, at one side thereof, with a fluid inlet, a plurality of accommodation spaces (112, 114) formed in the housing in a vertically stacked state such that a gap is defined between adjacent ones of the accommodation spaces (112, 114), a first channel formed between an uppermost one of the accommodation spaces (112, 114) and the housing, a second channel formed between a lowermost one of the accommodation spaces (112, 114) and the housing, and an intermediate channel formed at the gap, the first, second, and intermediate channels communicating with the fluid inlet; a discharge case spaced apart from the introduction case in a horizontal direction, the discharge case comprising a plurality of accommodation spaces (312, 314) defined in the discharge case, and a fluid outlet formed at one side of the discharge case; a connecting case arranged between the discharge case and the introduction case, a plurality of hollow fiber bundles extending through the accommodation spaces (112, 114) of the introduction case, an interior of the connecting case, and the accommodation spaces (312, 314) of the discharge case, to be accommodated therein; and barrier walls arranged to enclose the accommodation spaces (112, 114) such that the accommodation spaces (112, 114) are defined by the barrier walls, respectively, wherein a plurality of first introduction windows, a plurality of second introduction windows, and a plurality of intermediate windows to communicate the first, second, and intermediate channels (143, 144, 145) are formed at the barrier walls, to be arranged in a width direction of the barrier walls, wherein cross-sectional areas of the first and second channels (143, 144) are smaller than a cross-sectional area of the intermediate channel, wherein each of the first and second channels (143, 144) has a cross-sectional area gradually reduced in a direction from a channel end toward the fluid inlet to an opposite channel end.