To provide a noncondensable gas exhaust device for a condenser capable of preventing rubbing vibration of a turbine and shortening a vacuum degree adjusting time for the condenser.

The noncondensable gas exhaust device 20A has a first extraction amount regulating valve 2, a noncondensable gas extractor 3, a noncondensable gas extraction condenser 4 and a recoupler 5 installed at a noncondensable gas extraction pipe 21 from the condenser 1 side. A by-pass pipe 22 smaller in inner diameter than the noncondensable gas extraction pipe 21 is connected to the noncondensable gas extraction pipe 21. A second extraction amount regulating valve 8 installed at the by-pass pipe 22 has a smaller bore than the first extraction amount regulating valve 2. When adjusting the vacuum of the condenser, a controller 10 controls the opening of the second extraction amount regulating valve 8 based on the vacuum measured at a vacuum gauge 9 installed at the condenser 1.