A storage apparatus and its control method capable of implementing thin provisioning and reducing power consumption of storage devices are provided. The storage apparatus classifies a plurality of storage devices, which provide a pool with a storage resource, into a plurality of groups; performs thin provisioning operation by setting some of the plurality of groups to an active mode, in which the storage devices belonging to the groups are made to enter an activated state; sets other groups to a power-saving mode in which the storage devices are made to enter a power-saving state; and sequentially switches between the group(s) in the active mode and the group(s) in the power-saving mode among the plurality of groups.