An electrical power line insulator has an end clamp with a saddle for supporting an electrical wire, a track provided on a front surface of the saddle, a keeper for compressing and supporting an electrical wire seated in the saddle, a bolt and a nut for fastening the keeper to the saddle and operable to horizontally move the keeper along the track, and an insulator housing secured to the end clamp and mounted on a support structure. The end clamp and the insulator housing are detachably assembled with each other by means of a cylindrical clamp base integrally provided on a lower portion of the saddle and the track of the clamp and an upper fitting part. The upper fitting part has an assembly cylinder provided on an upper portion of the fitting part to be connected to the cylindrical clamp base, a compression cylinder provided on a lower portion of the fitting part and pressed against a post of the insulator housing, and a bolt and a nut fastening the cylindrical clamp base of the clamp to the assembly cylinder of the upper fitting part.