  We present deep spatially-resolved optical spectroscopy of the NW companion
galaxy of the quasar BR 1202-0725 at $z=4.7$. Its rest-frame UV spectrum shows
star-forming activity in the nuclear region. The Ly$\alpha$ emission profile is
symmetric with wavelength while its line width is unusually wide (FWHM $\simeq
1100$ km s$^{-1}$) for such a high-$z$ star-forming galaxy. Spectrum taken
along the Ly$\alpha$ nebula elongation, which is almost along the minor axis of
the companion host galaxy, reveals that off-nuclear Ly$\alpha$ nebulae have
either flat-topped or multi-peaked profiles along the extension. All these
properties can be understood in terms of superwind activity in the companion
galaxy. We also find a diffuse continuum component around the companion, which
shows similar morphology to that of Ly$\alpha$ nebula, and is most likely due
to scattering of the quasar light at dusty halo around the companion. We argue
that the superwind could expel dusty material out to the halo region, making a
dusty halo for scattering.
