To provide a polymer insulator wherein insulation property can be held surely over a long period of time.

This insulator 11 is provided with a rod 13 equipped with an umbrella-shaped outer cladding 12 on its outer circumferential surface and a mounting metal part 15 equipped with a mounting hole 19 into which an end part of this rod 13 is inserted. In this case, a seal member holding part 26, which is capable of holding a seal member 25, so as not to be exposed to the exterior, for putting a seal against rainwater seeping from the exterior into a boundary part 24 between the rod 13 and the mounting hole 19 of the mounting metal part 15, is provided on the mounting metal part 15 so as to stand opposite to an outer circumferential surface of the rod 13, and the seal member 25 is held in the seal member holding part 26.