A mount insulator is structured by a core metal body, installed at a fixed side and including an almost flat intermediate flange section having a piercing hole at an axial center section and a ring-shaped wall section extensively provided at the outer periphery of the intermediate flange in the direction of both sides crossing the intermediate section, and a mount elastic body section integrally fixed and formed with both sides of the intermediate flange section, an inner peripheral surface of the piercing hole and an inner peripheral surface of the ring-shaped wall section, and including an extension section expanded in a direction to cross the intermediate flange section and projecting from both wall sections, and a piercing supporting hole provided at the inner periphery side of the piercing hole of the intermediate flange section and piercing through between end surfaces of both extension sections of smaller diameter than that of the piercing hole and almost concentric with the piercing hole for piercingly support the axis section of a material to be mounted. Therefore, it is possible to restrict damaging of the mount insulator and generation of abnormal noise.