This ion exchange membrane has: a layer A that includes a fluorine-containing polymer that has a sulfonic acid group; and a layer B that includes a fluorine-containing polymer that has a carboxylic acid group. The ion exchange capacity of the layer B is 0.81 mEq/g or higher, and the value of (the ion cluster diameter of the layer B)/(the ion cluster diameter of the layer A) is 0.67-0.89.
