PURPOSE: To provide an image furnace, increased in the number of infrared rays projected against a material and improved in the efficiency thereof, in the image furnace wherein infrared rays, emitted from a heat source, are collected by a reflecting mirror to melt the material, grow the crystal and the like.

CONSTITUTION: A reflecting mirror, constituted of total five sets of reflecting surfaces of a turning ellipsoid 1a, arranged at the center thereof, turning ellipsoids 1d, 1e, arranged at the outer side thereof, and turning ellipsoids 1b, 1c, arranged at the outside of the turning ellipsoids 1d, 1e, is installed. According to this method, infrared rays, emitted from almost all of thermal light sources, are reflected repeatedly by the reflecting mirror and, thereafter, are projected against a specimen whereby the light collecting efficiency of the reflecting mirror when the ratio of the short diameter of the turning ellipsoid to the long diameter of that is small is improved.