A fluorine-containing polymer achieving both low resistivity and high thermal stability, which have been conventionally conflicting, a cation exchange membrane including the fluorine-containing polymer, and an electrolyzer including the cation exchange membrane. The cation exchange membrane including: the fluorine-containing polymer, which includes: a tetrafluoroethylene unit (A); and a perfluoroethylene unit (B) having a carboxylic acid-type ion exchange group, where the fluorine-containing polymer has a main-chain terminal structure (T) represented by the following formula (1):

—(CmFnH2m−n)—OH   (1)

in which m and n each represent any integer satisfying m≥2, n≥0, and 2m−n≥1.