A storage apparatus coupled to a host device comprises a virtual volume which is a virtual logical volume configured of multiple virtual areas and a pool configured of multiple actual area groups of different performances. A controller manages pool status information which is the information showing which actual area is allocated to which virtual area and access load related to the virtual areas. A management system of the storage apparatus, with reference to the pool status information at multiple points of time from past to present and an access load threshold which is equal to or larger than 1, estimates the used capacity of each actual area group at points of time in the future, calculates the installed/removed amount of each actual area group which is the difference between the estimated used capacity and the current storage capacity, and performs the processing based on the calculated result.