The present invention provides a movable defensive apparatus in which a
dedicated source of power for driving a relatively heavy defensive wall
and an installation space are not required, whereby entry of a mob, a
runaway vehicle, and the like, can be prevented, the entry of rainwater,
and the like, can also be prevented to some extent. The movable defensive
apparatus includes a defensive wall (2) disposed in the vicinity of a
doorway (O.cndot.I) of a site (G), such as a house, and an installation in
the vicinity of a doorway (O.cndot.I), a window or the like, of a building
for preventing rainwater and undesirable entry of objects, such as a mob
or a runaway vehicle from entering the site (g) or a building. Also
described is a piston cylinder unit (20, 20) which is operated by running
water for driving the defensive wall (2) from a machine room (M.cndot.R)
to a predetermined upper position along a guide device (10, 10).
