  Effects of the backward scattering with large momentum transfer are examined
in two-dimensional electron system with a special emphasis on electrons around
($\pi$,0), (0,$\pi$). The phase diagram is shown in the plane of temperature
$T$ and hole doping $\delta$ in the mean field approximation and it is found
that d-wave superconductivity, antiferromagnetism and $\pi$-triplet pair can
coexist near half filling.
