  We investigate long-term X-ray behaviors from the Sgr B2 complex using
archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra and ASCA. The
observed region of the Sgr B2 complex includes two prominent spots in the Fe I
K-$\alpha$ line at 6.40 keV, a giant molecular cloud M 0.66$-$0.02 known as the
``Sgr B2 cloud'' and an unusual X-ray source G 0.570$-$0.018. Although these
6.40 keV spots have spatial extensions of a few pc scale, the morphology and
flux of the 6.40 keV line has been time variable for 10 years, in contrast to
the constant flux of the Fe XXV-K$\alpha$ line at 6.67 keV in the Galactic
diffuse X-ray emission. This time variation is mostly due to M 0.66$-$0.02; the
6.40 keV line flux declined in 2001 and decreased to 60% in the time span
1994--2005. The other spot G 0.570$-$0.018 is found to be conspicuous only in
the Chandra observation in 2000. From the long-term time variability ($\sim$10
years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr
A$^*$ was X-ray bright in the past 300 year and exhibited a time variability
with a period of a few years.
