An objective of the present invention is to suppress bumping in the distillation still so as to collect a high purity solvent containing no impurities. A solvent vapor valve 21 is disposed in a solvent vapor withdrawal conduit 20 through which solvent vapor is transferred from inside the distillation still 10 to an inner pipe 31 of a double-tube structure 30 which is a heat exchange section. Also, a thermistor 14 is disposed in an upper space in the distillation still 10. After a heating chamber 11 starts heating the solvent, the start of boiling is determined by a sudden rise in temperature detected by the thermistor 14, and shortly thereafter, the solvent vapor valve 21 is closed to fill the distillation still 10 with the solvent vapor. The solvent vapor actively generated by bumping is condensed and liquefied on the cold inner surfaces of a ceiling wall and a sidewall of the distillation still 10, and concurrently, the heat of condensation is provided to the ceiling wall surface and the sidewall surface, thereby accelerating the temperature rise thereof. Bumping stops when the temperatures of the surfaces of the ceiling wall and the sidewall have reached a sufficiently high temperature, and thereafter the valve 21 is opened to transfer the solvent vapor to the double-tube structure 30 functioning as the heat exchange section.