To alleviate the stress generated in a lid member and a body of a cask due to the load of a moved fuel assembly.

In a fuel assembly storage cask 1 which has a bottomed body 2 whose upside is an opening and a lid member 4 for closing the opening and accommodates fuel assemblies 10 formed longitudinally with their longitudinal ends oriented toward the inner bottom face 22 of the body 2 of the cask 1 and the inner wall surface 41a of the lid member 4, convexes 100 that make intervals between the inner bottom face 22 of the body 2 of the cask 1 and the inner wall surface 41a of the lid member 4 and the ends of the fuel assemblies 10 different from those between them and the end of at least one fuel assembly 10 are placed in a region which is faced by the ends of the fuel assemblies 10 in the inner wall surface 41a of the lid member 4 and the load of the fuel assemblies 10 acting on the inner bottom face 22 of the body 2 of the cask 1 or the inner wall surface 41a of the lid member 4 is dispersed into more than one if external force is applied to each of the fuel assemblies 10 in a longitudinal direction.