PURPOSE: To make the filling density of an ion-exchange membrane high and the the size of the title apparatus small by forming a liquid flowing route continuously in a spiral shape.

CONSTITUTION: A module 2 has hollow pipes 6, 7 connected to the both ends of a bag-like ion-exchange membrane 3 in which a space 5 is set, and at the same time it is coild up spirally having another spacer 10 intermediately between the hollow pipe 6 and another hollow pipe 8. The module is packed in the inside of a container having liquid leading inlets 6, 12 and outlets 7, 8. An acidic or alkaline treatment solution is supplied to the hollow pipe 6 and the liquid leading inlet 12. As a result, filling density of the ion-exchange membrane is heightened and the size of the apparatus can be made small.