Shaking table model tests were conducted in order to reveal the stress on such a cylindrical steel caisson used for a seawall or a quaywall during earthquakes　The seawall model is composed of three pieces of steel-plate models which are connected by arc-plates with sand filling. The diameter, height and thickness of the steel-plate model are 900mm, 1100mm and 0.5mm respectively. In the tests, measurements were taken of the displacement and the stress of the steel-plate and the arc-plate, the response acceleration of the sand filling, the earth pressure at the base of sand filling, the backfill earth pressure, etc. As a result, it was revealed that most of backfill earth pressure and seismic force that act on the wall travel through the steel shell to the bottom slab and that it is conservative enough if the effective inertia coefficient of 0.8-1.0 in sand filling during earthquakes vibration is used for seismic design.