<p>A membrane element is disposed between a pair of water catchment cases. Inside each of the water catchment cases, there is provided a catchment space for collection of permeated liquid through the membrane element. A water catchment case of one membrane module is coupled via a coupling part with a water catchment case of other membrane module. The coupling part has a through-flow hole. The catchment space of a water catchment case of one membrane module communicates via the through-flow hole of the coupling part with the catchment space of a water catchment case of other membrane module.</p>
