  Stellar flares sometimes show red/blue asymmetries of H$\alpha$ line, which
can indicate chromospheric dynamics and prominence activations. However, the
origin of asymmetries is not completely understood. For a deeper understanding
of stellar data, we performed a Sun-as-a-star analysis of H$\alpha$ line
profiles of an M4.2-class solar flare showing dominant emissions from flare
ribbons by using the data of the Solar Dynamics Doppler Imager onboard the
Solar Magnetic Activity Research Telescope at Hida Observatory. The
Sun-as-a-star H$\alpha$ spectra of the flare show red asymmetry of up to
$\sim$95 km s$^{-1}$ and line broadening of up to $\sim$7.5 {\AA}. The
Sun-as-a-star H$\alpha$ profiles are consistent with spectra from flare regions
with weak intensity, but they take smaller redshift velocities and line widths
by a factor of $\sim$2 than those with strong intensity. The redshift
velocities, as well as line widths, peak out and decay more rapidly than the
H$\alpha$ equivalent widths, which is consistent with chromospheric
condensation model and spatially-resolved flare spectra. This suggests that as
a result of superposition, the nature of chromospheric condensation is
observable even from stellar flare spectra. The time evolution of redshift
velocities is found to be similar to that of luminosities of near-ultraviolet
rays (1600 {\AA}), while the time evolution of line broadening is similar to
that of optical white lights. These H$\alpha$ spectral behaviors in
Sun-as-a-star view could be helpful to distinguish whether the origin of
H$\alpha$ red asymmetry of stellar flares is a flare ribbon or other phenomena.
