A southwest region of the Carina nebula was observed with the Suzaku observatory for 47 ks in 2010 December. This region shows distinctively soft X-ray emission in the Chandra campaign observations. Suzaku clearly detects the diffuse emission above known foreground and background components between 0.4-5 keV at the surface brightness of 3.3x10^-14 erg s^{-1} arcmin^{-2}. The spectrum requires two plasma emission components with kT~0.2 and 0.5 keV, which suffer interstellar absorption of N_H~1.9x10^{21} cm^{-2}. Multiple absorption models assuming two temperature plasmas at ionization equilibrium or non-equilibrium are tested but there is no significant difference in terms of chi^2/d.o.f.. These plasma temperatures are similar to those of the central and eastern parts of the Carina nebula measured in earlier Suzaku observations, but the surface brightness of the hot component is significantly lower than those of the other regions. This means that these two plasma components are physically separated and have different origins. The elemental abundances of O, Ne and Mg with respect to Fe favor that the diffuse plasma originates from core-collapsed supernovae or massive stellar winds.
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