PURPOSE: To control the boundary shape of a crystalline material, thereby obtaining significantly uniform single crystals by providing pleural heating elements in the axial direction of a furnace, securing a temp. profile in a solidification region and controlling the heat transfer in the radial direction within the solidification region.

CONSTITUTION: The first and second heating elements 19, 23 isolately provided in the axial direction of the furnace 10 are translated along a crystalline sample 12 to form a liq. phase 16 and a solid phase 18 having temp. gradients with different inclinations. Further, a first gradient part 30 suited to the liq. phase 16 is provided to minimize the heat transfer in the radial direction from the liq. phase 16. Furthermore, a second gradient part 32 suited to the solid phase 18 is provided to minimize the heat transfer from the solid phase 18. Further, the materials with different coeffts. of thermal conductivity are used in order to control the thermal characteristic of the gradient parts 30, 32.