[Problem] Providing a storage apparatus and a snapshot control method for the same for preventing, even after long-term operation of snapshots as a means for backup, an increase in the amount of pre-update data retained in a differential volume.[Solution] According to this invention, snapshots utilizing pre-update data are replaced with snapshots utilizing update data so that the areas, in the differential volume, storing the pre-update data are released as free areas correspondingly, thereby avoiding accumulation of the pre-update data in the differential volume.