  We report new HI observations of the Type Ia supernova remnant SN 1006 using
the Australia Telescope Compact Array with an angular resolution of $4.5'
\times 1.4'$ ($\sim$2 pc at the assumed SNR distance of 2.2 kpc). We find an
expanding gas motion in position-velocity diagrams of HI with an expansion
velocity of $\sim$4 km s$^{-1}$ and a mass of $\sim$1000 $M_\odot$. The spatial
extent of the expanding shell is roughly the same as that of SN 1006. We here
propose a hypothesis that SN 1006 exploded inside the wind-blown bubble formed
by accretion winds from the progenitor system consisting of a white dwarf and a
companion star, and then the forward shock has already reached the wind wall.
This scenario is consistent with the single-degenerate model. We also derived
the total energy of cosmic-ray protons $W_\mathrm{p}$ to be only $\sim$1.2-$2.0
\times 10^{47}$ erg by adopting the averaged interstellar proton density of
$\sim$25 cm$^{-3}$. The small value is compatible with the relation between the
age and $W_\mathrm{p}$ of other gamma-ray supernova remnants with ages below
$\sim$6 kyr. The $W_\mathrm{p}$ value in SN 1006 will possibly increase up to
several 10$^{49}$ erg in the next $\sim$5 kyr via the cosmic-ray diffusion into
the HI wind-shell.
