We analyzed Suzaku data of Cygnus X-1 in the low/hard state, acquired on 25 occasions from 2005 to 2009, over 0.5-300 keV with a total exposure of ∼450 ks. Among the observations, its luminosity changed by a factor of ∼3. We found two different types of spectral changes in rather model independent manners. One is an increase of variability in E &lt
10 keV on time scales of days to months, revealed via a direct comparison among the 25 spectra. The other is a decrease of variability in E &lt
2 keV on time scales of 1-2 seconds, derived by using intensity-correlated spectral changes for each observation. The two spectral changes can be understood by considering that the accretion flow consists of a cool disk with a temperature of ∼0.2 keV surrounded by inhomogeneous coronae. © 2012 American Institute of Physics.