There is provided a copolymer containing tetrafluoroethylene unit and perfluoro(propyl vinyl ether) unit, wherein the copolymer has a content of perfluoro(propyl vinyl ether) unit of 4.9 to 5.7% by mass with respect to the whole of the monomer units, a melt flow rate at 372° C. of 45.0 to 55.0 g/10 min, and the number of functional groups of 50 or less per 106 main-chain carbon atoms.