Organic compound insualtor and its manufacture method

An organic composite insulator (tube) and method for production thereof giving an external flashover characteristic, enabling a reduction of the cost, and enabling a reduction of the size of the insulator. The outside diameters of the insulator sheath body and watersheds at only the intermediate insulator sheath 3c corresponding to the vicinity of the tip 6a of the top of the inside electrode 6 are made larger than the outside diameters of the body and watersheds of the upper and lower insulator sheaths 3a and 3b. The electric field of the sheath surface in the vicinity of the tip 6a of the top of the inside electrode 6 exhibiting the maximum electric field in the large size insulator is weakened and the maximum electric field part is moved to the top portion of the sheath body and watersheds enlarged in inside diameter. Further, the insulator act to block the propagation of the air dielectric breakdown occurring at the maximum electric field part to the ground side end fitting 2' and thereby to increase the external flashover voltage.