A heat insulation material obtained by sintering a raw material comprising: 52 to 93 weight % of alumina particles having an average particle diameter of 100 nm or smaller, 1 to 45 weight % of one or more crystal transition suppression materials selected from silica particles, silica stone, talc, mullite, silicon nitride, silica fume, wollastonite, bentonite, kaolin, sepiolite and mica particles, 0 to 40 weight % of a radiation scattering material, and 1 to 20 weight % of fibers.