  We present the results of a Suzaku spectroscopic study of the soft extended
X-ray emission in the HII region M17. The spectrum of the extended emission was
obtained with a high signal-to-noise ratio in a spatially-resolved manner using
the X-ray Imaging Spectrometer (XIS). We established that the contamination by
unresolved point sources, the Galactic Ridge X-ray emission, the cosmic X-ray
background, and the local hot bubble emission is negligible in the
background-subtracted XIS spectrum of the diffuse emission. Half a dozen of
emission lines were resolved clearly for the first time, including K lines of
highly ionized O, Ne, and Mg as well as L series complex of Fe at 0.5--1.5 keV.
Based on the diagnosis of these lines, we obtained the following results: (1)
the extended emission is an optically-thin thermal plasma represented well by a
single temperature of 3.0 +/- 0.4 MK, (2) the abundances of elements with
emission lines in the diffuse spectrum are 0.1--0.3 solar, while those of
bright discrete sources are 0.3--1.5 solar, (3) the metal abundances relative
to each other in the diffuse emission are consistent with solar except for a Ne
enhancement of a factor of 2, (4) both the plasma temperature and the chemical
composition of the diffuse emission show no spatial variation across the
studied spatial scale of about 5 pc.
