not blocked by the potting agent are communicated with the water collecting space hollow portion of the core an air dispersing plate a fig1 or 6 may be constituted by a conventional air dispersing tube or diffuser when the bundle of the hollow fiber membranes is used in vertical disposition the fluid generating means is preferably disposed on a lower water collecting plate from the view point of improvement of washing efficiency when a plurality of hollow fiber membrane modules are used it is preferable that the water collecting openings of the water collecting plates of the water collecting portions of the respective modules can be interconnected with this arrangement the plurality of hollow fiber membrane modules can be arranged efficiently as a result a suction means such as a pressure reducing pump used as a power source for filtration can be made compact and simple further it is desirable that a detachable socket member as shown in fig1 is attached to the water collecting opening regarding the water treating device using the hollow fiber membrane module according to the present invention the hollow fiber membrane module may be arranged in a horizontal or vertical disposition in the interconnection between the plurality of hollow fiber membrane modules as mentioned above by providing the detachable socket members as shown in fig1 on the water collecting openings of the water collecting plates the hollow.