The present invention concerns one of the plurality of first storage apparatuses, prior to a file migration to the second storage apparatus, notifies to the second storage apparatus of file migration information being information relating to the file migration, the second storage apparatus calculates an increment of a load on the second storage apparatus that is generated by the file migration based on information written in the file migration information, the second storage apparatus determines whether the file migration is allowable based on a current load on the second storage apparatus itself and the increment, the second storage apparatus notifies the determination result to the one of the plurality of first storage apparatuses that has notified the file migration information, and the one of the plurality of first storage apparatuses determines whether to migrate the file to the second storage apparatus based on the determination result.