To provide a method of manufacturing a fired body, in which a fired body easy in machining and free from the occurrence of damage or the deterioration of heat insulation effect if used at 1,200C can be obtained in the manufacture of a support for supporting heating device of a hot isotropic pressure device and a heat insulation structure.

The method of manufacturing the fired body used for the hot isotropic pressure device includes a molding step S1 of forming a mold 26 by impregnating woven fiber or unwoven fiber comprising a ceramic fiber, a first firing step S2 of firing a primary fired product 27 having 1.5-2.5 g/cm3 density by firing the mold 26 at 1,200C, a machining step S3 for machining the primary fired product and a second firing step S4 of obtaining a secondary fired product 28 as the fired body by firing the primary fired product after machining at 1,200C.