INSULATOR

Use of alumina cement mortar is enabled as a source material of a cement kneaded product cured body for joining hardwares onto an insulator body, whereby an insulator can maintain a high mechanical strength (initial strength, long-term strength) and a high electrical strength for a long period of time, and the curing time in forming the cured body is shortened to reduce the cost of producing the insulator. As a source material of a cement kneaded product cured body for joining hardwires one makes use of an alumina cement mortar obtained by kneading an alumina cement having a specific surface area of at least 3500 cm2/g, a polymer-steric-hindrance type water reducing agent, an aggregate, and water, or an alumina cement mortar obtained by kneading an alumina cement having an amorphous phase on an outer peripheral surface of particles and having a specific surface area of at least 3500 cm2/g, a water reducing agent, an aggregate, and water.