A storage system being coupled communicatively to an external device and providing a storage area to be used by the external device, comprising: a plurality of storage apparatuses (1100, 1200, 1300) of different performance capabilities, each having a storage medium that provides the storage area; and a storage controller holding: storage cost coefficients of the respective storage apparatuses, the storage cost coefficients being indices of utilization costs required in use of the respective storage apparatuses (1100, 1200, 1300), and being set in accordance with the performance capabilities of the respective storage apparatuses (1100, 1200, 1300); user cost allocation information for each user using the storage system from the external device, the user cost allocation information being an index of an available cost allocated to each user by an administrator; and user cost distribution information that defines, for each user proportions of the available cost allocated to the respective user that are allocated to each of the storage apparatuses (1100, 1200, 1300), wherein the storage controller is configured to: calculate, for each storage apparatus (1100, 1200, 1300) an ideal utilization for each user, based on the storage cost coefficients and the user cost distribution information, the ideal utilizations indicating an available capacity of the respective storage apparatus (1100, 1200, 1300) for the respective user; when additional file data of a user is received, store the additional file data of the user to the storage apparatus having the highest performance capability if a total amount of the additional file data and data of the user already stored in the storage apparatus having the highest performance capability is equal or less than the ideal utilization of the user for the storage apparatus having the highest performance capability and if the total amount of the additional file data is also equal or less than a free space amount of the storage apparatus; and when data of the user is deleted from a storage apparatus of the plurality of storage apparatuses (1100, 1200, 1300), migrate at least one file of the user stored in a storage apparatus (1200, 1300) having a lower performance capability than the storage apparatus from which the data is deleted to the storage apparatus from which the data is deleted. a plurality of storage apparatuses (1100, 1200, 1300) of different performance capabilities, each having a storage medium that provides the storage area; and a storage controller holding: storage cost coefficients of the respective storage apparatuses, the storage cost coefficients being indices of utilization costs required in use of the respective storage apparatuses (1100, 1200, 1300), and being set in accordance with the performance capabilities of the respective storage apparatuses (1100, 1200, 1300); user cost allocation information for each user using the storage system from the external device, the user cost allocation information being an index of an available cost allocated to each user by an administrator; and user cost distribution information that defines, for each user proportions of the available cost allocated to the respective user that are allocated to each of the storage apparatuses (1100, 1200, 1300), wherein the storage controller is configured to: storage cost coefficients of the respective storage apparatuses, the storage cost coefficients being indices of utilization costs required in use of the respective storage apparatuses (1100, 1200, 1300), and being set in accordance with the performance capabilities of the respective storage apparatuses (1100, 1200, 1300); user cost allocation information for each user using the storage system from the external device, the user cost allocation information being an index of an available cost allocated to each user by an administrator; and user cost distribution information that defines, for each user proportions of the available cost allocated to the respective user that are allocated to each of the storage apparatuses (1100, 1200, 1300), wherein the storage controller is configured to: calculate, for each storage apparatus (1100, 1200, 1300) an ideal utilization for each user, based on the storage cost coefficients and the user cost distribution information, the ideal utilizations indicating an available capacity of the respective storage apparatus (1100, 1200, 1300) for the respective user; when additional file data of a user is received, store the additional file data of the user to the storage apparatus having the highest performance capability if a total amount of the additional file data and data of the user already stored in the storage apparatus having the highest performance capability is equal or less than the ideal utilization of the user for the storage apparatus having the highest performance capability and if the total amount of the additional file data is also equal or less than a free space amount of the storage apparatus; and when data of the user is deleted from a storage apparatus of the plurality of storage apparatuses (1100, 1200, 1300), migrate at least one file of the user stored in a storage apparatus (1200, 1300) having a lower performance capability than the storage apparatus from which the data is deleted to the storage apparatus from which the data is deleted.