PURPOSE: To continuously purify a solvent having high boiling point under atmospheric pressure by using a pallet type pump comprising a rotor and a stator as a vacuum pump and installing the whole of the pump inside a tank filled with the same solvent as the one to be purified.

CONSTITUTION: This apparatus is provided with a distillation unit 4 to whose bottom the solvent 6 to be purified is supplied from used apparatus 1 and a vacuum pump 5 which can send a distillate obtained by distillation and whose suction port is connected to a distillate collecting zone 9 of the distillation unit 4 and then whose discharging port is connected to a pipe line 2 for returning the solvent to the used apparatus 1. The vacuum pump 5 is a pallet type pump comprising a functional assembly provided with the rotor 11 and the stator 12 and the assembly is installed in the tank 13 filled with a lubricating liquid being the same solvent 6A as the solvent 6. In this apparatus, there is no risk to contaminate the solvent purified and sent to the used apparatus 1 through the return pipe line 2 and the solvent having 150°C or higher boiling point under atmospheric pressure can be continuously purified.