  We discovered a new growth mode of dust grains to km-sized bodies in
protoplanetary disks that evolve by viscous accretion and magnetically driven
disk winds (MDWs). We solved an approximate coagulation equation of dust grains
with time-evolving disks that consist of both gas and solid components by a
one-dimensional model. With the grain growth, all solid particles initially
drift inward toward the central star by the gas drag force. However, the radial
profile of gas pressure, $P$, is modified by the MDW that disperses the gas in
an inside-out manner. Consequently, a local concentration of solid particles is
created by the converging radial flux of drifting dust grains at the location
with the convex upward profile of $P$. When the dimensionless stopping time,
${\rm St}$, there exceeds unity, the solid particles spontaneously reach the
growth dominated state because of the positive feedback between the suppressed
radial drift and the enhanced accumulation of dust particles that drift from
the outer part. Once the solid particles are in the drift limited state, the
above-mentioned condition of ${\rm St} \gtrsim 1$ for the dust growth is
equivalent with \begin{equation}
  \Sigma_{\rm d}/\Sigma_{\rm g}\gtrsim \eta, \nonumber \end{equation} where
$\Sigma_{\rm d}/\Sigma_{\rm g}$ is the dust-to-gas surface-density ratio and
$\eta$ is dimensionless radial pressure-gradient force. As a consequence of the
successful growth of dust grains, a ring-like structure containing
planetesimal-sized bodies is formed at the inner part of the protoplanetary
disks. Such a ring-shaped concentration of planetesimals is expected to play a
vital role in the subsequent planet formation.
