AROMATIC SULFONIC ACID DERIVATIVE, SULFONIC ACID GROUP-CONTAINING POLYMER, BLOCK COPOLYMER, POLYMER ELECTROLYTE MATERIAL, POLYMER ELECTROLYTE FORM ARTICLE, AND POLYMER ELECTROLYTE FUEL CELL

Provided are an aromatic sulfonic acid derivative and a sulfonic acid group-containing polymer, each of which has excellent proton conductivity even under low humidification conditions, while having excellent mechanical strength and chemical stability, and enables a solid polymer fuel cell to achieve high output and excellent physical durability when used therein. This aromatic sulfonic acid derivative has a specific structure and is characterized in that a sulfonic acid group is introduced into more than 50% of all the phenyl groups. This sulfonic acid group-containing polymer is characterized by being obtained by polymerization using the aromatic sulfonic acid derivative, and is also characterized by having a specific structure.