PURPOSE: To separate impurities such as a residual solvent with which a solid sample is impregnated securely on a dry basis by heating an impurity separating device directly or by a reaction treatment.

CONSTITUTION: This device consists of a main separating device body 2 whose one end part is closed and a sample chamber 3 at one end part side in it, and a heating device 4 is arranged at the outer peripheral part of one end of the main body 2 while covering the sample chamber 3. Consequently, the solid sample is put in the sample chamber 3, which is heated up to necessary internal temperature while the inside of the sample chamber is held below constant pressure when impurities are separated below 200°C without any heat destruction or in a pressure reduction state by a pressure reducing device 22 when not. The heating is stopped when the specific temperature 18 is obtained in the sample chamber 3 and the time required for the impurities sticking on the solid sample to separate is elapsed sufficiently. A flow rate control valve 10 is controlled and opened and carrier gas 7 is supplied through a gas supply pipe 13. Consequently, the low-density impurities of specific level which stick on the solid sample are separated and a high-purity solid sample is obtained.