PURPOSE: To synthesize a Cd compd. contg. no impurity with high yield by adding Cd portionwise in a small amt. in the form of liquid drop to a melted group VI element in the stage of synthesizing a compd. of Cd with a group VI element.

CONSTITUTION: A crucible 1 is placed in a vessel 5, and a molten body 2 of a group VI element such as Te, Se, S, etc., is formed by heating with a main heater 4, and the surface of the melt is covered with molten B2O3. Solid Cd 12 is fed to an ampule 7 at the top of the vessel and heated with a subheater 8 to melt Cd having low melting point, and the vapor of Cd is introduced into a refluxing device 9 at the top of the vessel. The Cd vapor rises upward through a first zone 15 of the refluxing device, enters a second zone 16 through a perforated hole 18, raised upward, further, through the third zone 17, where it is transformed to liquid by cooling, but a part is vaporized again by being heated by the vapor of Cd from the ampule 7 and raised to the top 10 of the device. The vapor enters a communicating pipe 11 at the side part, and enters a liquid phase 2 of Te, etc., in the form of liquid drops, etc., by being liquefied and rises through the liquid Te 2 in the form of fine foams. During this stage, the vapor forms a CdTe compd. in high yield.