A high thermal conduction insulator exhibiting thermal conductivity, insulating properties and heat radiating properties is produced by supplying a molding material composed of an insulating resin, a diamagnetic material powder and a paramagnetic material (inclusive of ferromagnetic material) powder, and exhibiting fluidity into a mold, and applying a magnetic field to the molding material in the mold to orient clusters, each being composed of diamagnetic material particles of the diamagnetic material powder, which are joined together like a chain, along directions of lines of a magnetic force, and draw the paramagnetic material (inclusive of ferromagnetic material) powder with the magnetic force along one of mold surfaces of the mold, thereby forming a heat radiating layer. Heat transmitted from a facing member to one surface of the insulator is speedily transmitted to the other surface thereof via the clusters, and is effectively radiated from the heat radiating layer existing in the other surface.