Membrane separation method and a membrane separation device

Disposed bubbles guide 30 between the flat membranes 20 and 20 adjacent in the arrangement direction, the bubble guide 30 facing to the flat film 20, a plurality in the direction perpendicular to the arrangement direction extends in the vertical direction forming a hollow closed cross section 50 lined with the bubbles by aeration, so as to flow the closed cross section 50 consisting of a flat membrane 20 and the bubble guide 30 as the flow path 60, facing in parallel as in the prior art compared to what the bubbles flowing bubbles in a wide flow passage between the flat film with each other can not be washed entirely with uniformly strong force without contacting the entire membrane surface, the membrane surface by air bubbles flowing through the narrow flow passage 60 the whole efficiently washed uniformly strong force.