Temperature distribution in a cylindrical furnace used in a high‐pressure apparatus has been calculated by the difference method. The calculated values are in good agreement with the experimental observations obtained by an x‐ray diffraction method. A steep temperature gradient exists in a simple cylindrical furnace. In order to obtain a homogeneous temperature distribution, a furnace composed of a graphite tube and two graphite disks has been designed. It has been demonstrated that a homogeneous temperature distribution can be obtained by selecting proper resistivities for the tube and the disks. The design requires a large power input, which could result in a shorter lifetime of the anvils.