PURPOSE: To prevent the exterior of the tank from being corroded by a constitution wherein the upper surface of the heat molten material tank, the exterior or which is covered with heat insulating material, is titled and water drops fallen on the upper surface of the tank are led through gutters to a bilge tank located at a double bottom.

CONSTITUTION: The heat molten material tank 10 to transport sulfur, asphalt or the like is covered with the heat insulating material 14 ranging nearly over its whole exterior. The upper surface of the tank 10 is titled longitudinally and transversely with the central part of the tank at its apex. Only the upper surface of the tank 10 is covered with high temperature proof and waterproof material 13 such as galvanized sheet or the like and furthermore the gutter shape water passages 8 are provided around the tank. According to the constitution as described above, the water drops fallen on the upper surfaces of the tank is led, through the titled surface and the gutter shape water passages 8, to the bilge tank located at a double bottom.