Provided is a method of managing differential snapshots in a storage system, the storage system having a disk drive and a disk controller, the differential snapshot management method including the steps of: providing a storage area of the disk drive as a plurality of logical volumes including an operational volume and a differential volume; storing a time of update for each block in the operational volume; and judging, upon reception of a request to write in a block included in the operational volume, whether to copy data of the block in which requested data is to be written in accordance with the received write request to the differential volume, based on the time of update of the block in which requested data is to be written and a time of creation of the differential snapshot. Accordingly, it is possible to manage the differential snapshot without using a bitmap.