  The Crab Nebula is one of the brightest and most stable sources in the X-ray
sky. Year-scale flux variation from the object was recently revealed in the
hard X-ray band by four satellites. This marked the first detection of
year-scale variability from pulsar wind nebulae in the hard X-ray band. The
Crab Nebula has been observed at least once a year for calibration purposes
with the Suzaku Hard X-ray Detector (HXD) since its launch in 2005. In order to
investigate possible spectral changes as well as flux variation, the archival
data of the HXD were analyzed. The flux variation reported by other instruments
was confirmed in the 25 -- 100 keV band by the HXD in a few percent level, but
flux above 100 keV did not follow the trend in variation below 100 keV. The
hardness ratios produced utilizing the PIN and GSO sensors installed in the HXD
exhibit significant scattering, thereby indicating spectral variations in the
hard X-ray. The spectral changes are quantified by spectral fitting with a
broken power-law model. The difference between the two photon indexes of the
broken power-law model in harder and softer energy bands is in the range of <
2.54. Taking into account flux variation of 6.3% and spectral variation
time-scale of a few days, multi components of the broken power-law-shaped
synchrotron emission with different cooling times are suggested.
