A catalyst layer comprising a supported catalyst having a carrier containing a metal oxide, and a catalyst supported on the carrier, and a polymer having at least one type of units containing a cyclic ether structure, selected from the group consisting of units represented by the formula, units represented by the formula, units represented by the formula and units represented by the formula, and having ion exchange groups, wherein the total of the content of the units containing the cyclic ether structure is at least 30 mol% to all units which the polymer contains: in the formula, R 11 is a divalent perfluoroorganic group which may have an ether-bonding oxygen atom, and R 12, R 13, R 15 and R 16 are each independently a monovalent perfluoroorganic group which may have an ether-bonding oxygen atom, or a fluorine atom, R 14 is a monovalent perfluoroorganic group which may have an ether-bonding oxygen atom; a fluorine atom; or a group represented by -R 11 (SO 2 X(SO 2 R f) a) - M +, where M + is H +, a monovalent metal cation, or an ammonium ion in which at least one hydrogen atom may be substituted by a hydrocarbon group, and R f is a linear or branched perfluoroalkyl group which may have an ether-bonding oxygen atom, X is an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a = 0, when X is a nitrogen atom, a = 1, and when X is a carbon atom, a = 2; in the formula, R 21 is a C 1-6 perfluoroalkylene group, or a C 2-6 perfluoroalkylene group having an ether-bonding oxygen atom between carbon-carbon bonds, and R 22 is a fluorine atom, a C 1-6 perfluoroalkyl group, a C 2-6 perfluoroalkyl group having an ether-bonding oxygen atom between carbon-carbon bonds, or a group represented by -R 21 (SO 2 X(SO 2 R f) a) - M +, where M +, R f and X are the same as above; in the formula, R 41, R 42, R 43, R 44, R 45 and R 46 are each independently a monovalent perfluoroorganic group which may have an ether-bonding oxygen atom, or a fluorine atom; in the formula, s is 0 or 1, R 51 and R 52 are each independently a fluorine atom, a C 1-5 perfluoroalkyl group, or a spiro ring formed by linking with each other (provided in the case where s is 0), R 53 and R 54 are each independently a fluorine atom, or a C 1-5 perfluoroalkyl group, and R 55 is a fluorine atom, a C 1-5 perfluoroalkyl group, or a C 1-5 perfluoroalkoxy group. a supported catalyst having a carrier containing a metal oxide, and a catalyst supported on the carrier, and a polymer having at least one type of units containing a cyclic ether structure, selected from the group consisting of units represented by the formula, units represented by the formula, units represented by the formula and units represented by the formula, and having ion exchange groups, wherein the total of the content of the units containing the cyclic ether structure is at least 30 mol% to all units which the polymer contains: in the formula, R 11 is a divalent perfluoroorganic group which may have an ether-bonding oxygen atom, and R 12, R 13, R 15 and R 16 are each independently a monovalent perfluoroorganic group which may have an ether-bonding oxygen atom, or a fluorine atom, R 14 is a monovalent perfluoroorganic group which may have an ether-bonding oxygen atom; a fluorine atom; or a group represented by -R 11 (SO 2 X(SO 2 R f) a) - M +, where M + is H +, a monovalent metal cation, or an ammonium ion in which at least one hydrogen atom may be substituted by a hydrocarbon group, and R f is a linear or branched perfluoroalkyl group which may have an ether-bonding oxygen atom, X is an oxygen atom, a nitrogen atom, or a carbon atom, and when X is an oxygen atom, a = 0, when X is a nitrogen atom, a = 1, and when X is a carbon atom, a = 2; in the formula, R 21 is a C 1-6 perfluoroalkylene group, or a C 2-6 perfluoroalkylene group having an ether-bonding oxygen atom between carbon-carbon bonds, and R 22 is a fluorine atom, a C 1-6 perfluoroalkyl group, a C 2-6 perfluoroalkyl group having an ether-bonding oxygen atom between carbon-carbon bonds, or a group represented by -R 21 (SO 2 X(SO 2 R f) a) - M +, where M +, R f and X are the same as above; in the formula, R 41, R 42, R 43, R 44, R 45 and R 46 are each independently a monovalent perfluoroorganic group which may have an ether-bonding oxygen atom, or a fluorine atom; in the formula, s is 0 or 1, R 51 and R 52 are each independently a fluorine atom, a C 1-5 perfluoroalkyl group, or a spiro ring formed by linking with each other (provided in the case where s is 0), R 53 and R 54 are each independently a fluorine atom, or a C 1-5 perfluoroalkyl group, and R 55 is a fluorine atom, a C 1-5 perfluoroalkyl group, or a C 1-5 perfluoroalkoxy group.