  We examine the possibility of the active galactic nucleus (AGN) obscuration
by dusty gas clouds that spurt out from circumnuclear starburst regions. For
the purpose, the dynamical evolution of gas clouds is pursued, including the
effects of radiation forces by an AGN as well as a starburst. Here, we solve
the radiative transfer equations for clouds, taking into consideration the
growth of clouds by inelastic cloud-cloud collisions and the resultant change
in optical depth. As a result, it is shown that if the starburst is more
luminous than the AGN, gas clouds are distributed extensively above a galactic
disk with the assistance of radiation pressure from the starburst. The total
covering factor of gas clouds reaches a maximum of around 20%. After several
$10^{7}$yr, gas clouds with larger optical depth form by cloud-cloud collisions
and thereafter the clouds fall back due to weakened radiation pressure. The
larger clouds undergo runaway growth and are eventually distributed around the
equatorial plane on the inner sides of circumnuclear starburst regions. These
clouds have an optical depth of several tens. The result is qualitatively
consistent with the putative tendency that Seyfert 2 galaxies appear more
frequently associated with starbursts than Seyfert 1s. On the other hand, if
the AGN luminosity overwhelms that of the starburst, almost all clouds are
ejected from the galaxy due to the radiation pressure from the AGN, resulting
in the formation of a quasar-like object. The origin of obscuration of AGNs is
discussed with relevant observations.
