To provide a polytetrafluoroethylene insulator small in a dielectric loss tangent in a high-frequency band 1 GHz.

This polytetrafluoroethylene insulator is manufactured by a manufacturing method including a process of irradiating a material containing polytetrafluoroethylene with a -ray having an exposure of 100-3,000 Gy. In the manufacturing method, a process of providing the polytetrafluoroethylene insulator is preferably executed by processing the material irradiated with the -ray into a desired shape, and a process of baking the polytetrafluoroethylene insulator is preferably further executed.