To provide a treatment method for an inorganic salt-containing waste liquid which produces an acid solution usable as a flocculant from at least one part of the acid solution which is formed when the inorganic salt-containing waste liquid is treated by an electrodialyzer apparatus having a bipolar membrane.

A treatment method for an inorganic salt-containing waste liquid includes supplying an inorganic salt-containing waste liquid to an electrodialyzer apparatus having a bipolar membrane, to take out an acid solution and an alkali solution, wherein at least one part of the acid solution is contacted with a metal or a metal compound to form a metal salt solution for flocculation treatment. The metal as the metal and the metal compound is suitably iron and/or aluminum. A polyvalent metal ion may be removed from a feeding liquid to the electrodialyzer apparatus.