PROBLEM TO BE SOLVED: To provide an easy and low-cost radioactive substance storage method capable of storing a radioactive substance without being affected by the ground and terrain of a storage area, and a cylindrical structure used for the method.SOLUTION: In a radioactive substance storage method, a radioactive substance stored in a container is placed in a cylindrical structure formed by a geogrid, and the inside of the structure is filled with a filler. Preferably, an inner surface and/or an outer surface of the cylindrical structure are covered with a sheet-like object.