To solve a problem that cracks is easily developed from a breaking start point of the outer surface to easily cause breaking by receiving mechanical impact from the outside and the impact strength is decreased becuase the crack is easily developed from the crack starting point of the outer surface by receiving mechanical impact from the outer surface when the compressive stress in the direction vertical to the thickness direction of the outer surface of the ceramic hollow body is low.

The ceramic hollow body 1 is a ceramic hollow body 1 having a closed space 10 inside and the open porosity in the outer surface 12 is higher than that in the inner surface 11 in contact with the closed space 10. As a result the hollow body having high impact strength and the buoy material using the same are provided and further excellent submerging apparatus and the buoy for molten metal are provided.