A hollow fiber membrane module for an external pressure filtration for raw water, comprising: a hollow fiber membrane bundle including bundled hollow fiber membranes; a housing formed with a port for allowing a cleaning gas for cleaning the hollow fiber membrane bundle to inflow therethrough for accommodating the hollow fiber membrane bundle; and a diffuser including a disc-shaped main body and a partition, the main body having a receiving surface for receiving the cleaning gas having entered through the port, the partition having an upper end connected to the receiving surface so as to be concentric with the main body, the receiving surface being formed with a plurality of diffusion holes for diffusing the cleaning gas to the hollow fiber membrane bundle in the housing such that the cleaning gas forms bubbles which encounter the hollow fiber membranes causing any suspended solids deposited on the hollow fiber membranes to fall off, and a water flow pipe arranged in the housing, the water flow pipe penetrating through a center of the diffuser and vertically extending in an inside space defined by the hollow fiber membrane bundle, wherein the main body having a through hole at a center thereof, the water flow pipe being inserted in the through hole, the partition has a cylindrical shape with a diameter larger than that of the through hole, the partition divides a space under the receiving surface into an inner space and an outer space surrounding the inner space and permits the cleaning gas having entered through the port to flow into the outer space, and the plurality of diffusion holes include a plurality of inner diffusion holes communicating with the inner space and are arranged to allow at least a part of the cleaning gas flowing in the outer space to diffuse to the hollow fiber membrane bundle through the inner space, the plurality of inner diffusion holes being at intervals in radial and circumferential directions. a hollow fiber membrane bundle including bundled hollow fiber membranes; a housing formed with a port for allowing a cleaning gas for cleaning the hollow fiber membrane bundle to inflow therethrough for accommodating the hollow fiber membrane bundle; and a diffuser including a disc-shaped main body and a partition, the main body having a receiving surface for receiving the cleaning gas having entered through the port, the partition having an upper end connected to the receiving surface so as to be concentric with the main body, the receiving surface being formed with a plurality of diffusion holes for diffusing the cleaning gas to the hollow fiber membrane bundle in the housing such that the cleaning gas forms bubbles which encounter the hollow fiber membranes causing any suspended solids deposited on the hollow fiber membranes to fall off, and a water flow pipe arranged in the housing, the water flow pipe penetrating through a center of the diffuser and vertically extending in an inside space defined by the hollow fiber membrane bundle, wherein the main body having a through hole at a center thereof, the water flow pipe being inserted in the through hole, the partition has a cylindrical shape with a diameter larger than that of the through hole, the partition divides a space under the receiving surface into an inner space and an outer space surrounding the inner space and permits the cleaning gas having entered through the port to flow into the outer space, and the plurality of diffusion holes include a plurality of inner diffusion holes communicating with the inner space and are arranged to allow at least a part of the cleaning gas flowing in the outer space to diffuse to the hollow fiber membrane bundle through the inner space, the plurality of inner diffusion holes being at intervals in radial and circumferential directions.