PURPOSE: To obtain a high vacuum by a method wherein a solution is utilized as a driving liquid instead of water.

CONSTITUTION: In case the solution of ethylene glycol is utilized instead of water as the driving liquid, a suction vacuum may be obtained until the vapor pressure of water in each temperatures by reducing the temperature of the solution to a temperature below 0°C. In case organic or inorganic liquid such as saline solution of some concentration, low viscosity oil or the like except ethylene glycol, which are not frozen at a temperature below 0°C, is utilized, the vacuum at least below 6W7Torr, in some case the same near 1Torr, may be obtained by the suction of the pump.