An image forming apparatus which can prevent from automatically deleting, without user's intention, a box document restored from another image forming apparatus. A document storage deadline is set with respect to a folder thereof for storing box documents so as to set, as a target to be deleted from the folder, a box document having been stored in the folder over the document storage deadline. When it is determined that one of the box documents stored in the folder is a restored document, the one of the box documents is controlled to be excluded from the target.