PURPOSE: To provide a steep temperature-gradient by a method wherein at one end part in a high temperature section, a high load density heating unit is provided, and a cooling unit is detachably provided between the high temperature section and a low temperature section.

CONSTITUTION: A high temperature section and low temperature section consist of 3 zones, and a high temperature uniform section 5 consisting of one heater H1, and another high load density temperature section 7 consisting of a heater H2 under the high temperature uniform section 5 are provided, and those sections constitute an electric furnace. Under the electric furnace, a cooling body 10 with a water-cooling structure is arranged, and this interval is changed for the structure. In addition, a low temperature section 12 consisting of one heater H3 is arranged under the cooling body 10. For these heating units, thermocouples 6, 8, 13 for temperature control are respectively arranged, and are controlled at set temperatures by respective temperature regulators. By this method, a steep temperature gradient of 80°C/cm can be obtained.