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.
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