Membrane filtration device and control method thereof

The present invention provide a film filtering device capable of reliably backflushing, preventing reduction of filtering efficiency and increase of transferring cost of the film filtering device, and capable of steadily and adequately ensuring filtering water volume. The film filtering device (S1) repeats filtering of set time and backflushing of set times in a plurality of film filtering units (A, B, C) for separating dispersant and dispersate, the backflushing of set times execute set on the filtering units (A, B, C) according to degree of the dispersate in the filtering unit (A, B, C) accumulated because of the filtering of set time, the film filtering device (S1) is characterized in when backflushing starting times of the filtering units (A, B, C) overlaps, the backflushing of the filtering units are carried out according to order with fewer backflushing times.