To provide a concrete cask that can more securely prevent the toppling of the cask caused by an earthquake.

After an intermediate part 9 of a cask is put on a bottom part 8 of the cask formed as one body together with a floor slab 7 and an object to be stored is housed in the space inside the cask, an upper part 10 of the cask 2 is put on the intermediate part 9 of it. Then, the upper part 10 of the cask and the intermediate part 9 of it are fastened to the bottom part 8 formed as one body together with the floor slab 7 to more securely prevent a concrete cask from toppling by inserting fixing bolts 11 into bolt holes of the upper part 10 of the cask and intermediate one 9 of it and screwing the fixing bolts 11 onto screw holes of the bottom part 8.