Provided is a functional polymer membrane having a structure represented by the following Formula (1) and a structure represented by the following Formula (2), in which an ion exchange capacity is 2.0 meq/g to 7.0 meq/g; and a method for producing the same, —S-LL1-LL-LL2-S—   Formula (1) in Formula (1), LL represents a single bond or an alkylene group which may have a substituent, —O—, —S—, —NRZ— or a linking group obtained by combining these, LL1 and LL2 represent —(CR1R2)I— or —(CR1R2)I—C(═O)O— (in which the atom bonded to LL is an oxygen atom), R1 and R2 represent a hydrogen atom or an alkyl group, I represents 1 or 2, RZ represents a hydrogen atom or a substituent, however, in a case where terminal atoms of a substituent in LL and a substituent of RZ are a sulfur atom, LL is the sulfur atom having a bond to be incorporated into the polymer chain, and in Formula (2), L1 represents an alkylene group or an alkenylene group, Ra, Rb, Rc, and Rd each independently represent an alkyl group or an aryl group, Ra and Rb, or/and Rc and Rd may be bonded to each other to form a ring, n1 represents an integer of 1 to 10, and X1− and X2− each independently represent an organic or inorganic anion.