There is provided an apparatus for suppressing sloshing. An apparatus for suppressing sloshing according to an embodiment of the present invention includes a plurality of buoyant blocks and connecting members connecting the buoyant blocks and can float on a liquid cargo in a liquid cargo storage tank, the buoyant block includes a buoyant body having buoyancy to float on liquid, a first foam member covering the buoyant body and absorbing the liquid, and a first cover covering the first foam member, and the first foam member has through-holes formed through the first foam member.