  We report X-ray spectroscopic results for four giant solar flares occurred on
2005 September 7 (X17.0), 2005 September 8 (X5.4), 2005 September 9 (X6.2), and
2006 December 5 (X9.0), obtained from Earth albedo data with the X-ray imaging
spectrometer (XIS) onboard Suzaku. The good energy resolution of the XIS
(FWHM$\sim$100 eV) enables us to separate a number of line-like features and
detect the underlying continuum emission. These features include Si He$\alpha$,
Si Ly$\alpha$, S He$\alpha$, S Ly$\alpha$, Ar He$\alpha$, and Ca He$\alpha$
originating from solar flares as well as fluorescent Ar K$\alpha$ and Ar
K$\beta$ from the Earth atmosphere. Absolute elemental abundances (X/H)
averaged over the four flares are obtained to be $\sim$2.0 (Ca), $\sim$0.7
(Si), $\sim$0.3 (S), and $\sim$0.9 (Ar) at around flare peaks. This abundance
pattern is similar to those of active stars' coronae showing inverse first
ionization potential (i-FIP) effects, i.e., elemental abundances decrease with
decreasing FIP with a turnover at the low end of FIP. The abundances are almost
constant during the flares, with an exception of Si which increases by a factor
of $\sim$2 in the decay phase. The evolution of the Si abundance is consistent
with a picture that the i-FIP plasma originates from the chromosphere
evaporation and then mixes with the surrounding low-FIP biased materials.
Flare-to-flare abundance varied by a factor of 2, agreeing with past
observations of solar flares. Finally, we emphasize that Earth albedo data
acquired by X-ray astronomy satellites like Suzaku and XRISM can significantly
contribute to studies of solar physics.
