To reduce damage to vertically communicating partition walls in wide sections when side collision happens to laterally residing partition walls in a hull, on which a cargo handling area is partitioned with several laterally residing partition walls where independent tanks are set up, by providing the vertically communicating partition walls at given positions in sections adjacent to either the front or the rear of the laterally residing partition walls.

A cargo handling area 2 in a hull 1 is partitioned with several laterally residing partition walls 3 to form independent tanks 4. The independent tank 4 in a cargo handling area 21 is formed at the maximum width, as a void space in a section 7 at both starboard and port or the minimum width enough to do constructing work for a ballast tank is left, and divided into both starboard and port tanks. The section 7 is encircled by the laterally residing partition wall 3, an outer plate 6 and a vertically communicating partition wall 5 at both starboard and port sides of the independent tank 4. On the other hand, the independent tanks 4 in the cargo handling areas 22, 23, which have the front parts in the longitudinal direction with a width to be about 3/5 of a ship width and the rear parts with the maximum width as the minimum width is left, are divided into both starboard and port tanks. A section 7' which has a width to be about 1/5 of the ship width is encircled by the laterally residing partition wall 3, the outer plate 6 and a vertically communicating partition wall 5'.