PURPOSE: To simplify the structure omitting a vacuum gage and achieve downsizing of a pressure switch provided with a heating means by constructing it using a shape memorizing alloy.

CONSTITUTION: By actuating a pump for low vacuum 5, back pressure of a pump 3 for high vacuum is reduced. By electrifying a shape memorizing alloy 15 of a pressure switch 2 by a power source 18, the shape memorizing alloy 15 is heated, which is then deformed against a spring 16 at the temperature greater than the predetermined, and is extended in the direction indicated by an arrow. A movement contact 17 is also moved downward at this time until it contacts a fixed contact 14A, whereby, the pressure switch 2 is turned 'ON', and based on a working signal from a driving device 6, the pump for high vacuum 3 is actuated. When the pump 3 for high vacuum is actuated, pressure in a pressure reduction container 1 is further reduced.