PURPOSE: To prevent sealing performance from being damaged with simple structure when a container is subjected to impact such as falling regardless of the kind of sealant.

CONSTITUTION: A bolt insertion hole 26 is provided for the outer circumferential section of a cover 12, and a bolt 30 is inserted therein, so that the cover 12 is fastened to a container main body 10. A groove 32 which is cut in the plate thickness direction of the cover 12, is formed in the cover 12 at a position in the side inner than the bolt insertion hole 26 in the radial direction, and radioactive shielding material composed of material lower in stiffness than that of the cover 12, is then filled up in the inside of the groove 32.