The fact that data stored in a storage system is not updated for a given period is proven to a third party. A method of managing data that is given an update prohibitive attribute includes a step of storing, in a management server, information on an end time of the update prohibitive attribute which is received from a storage system, a step of receiving, from the storage system, a request for permission to change the update prohibitive attribute given to the data and obtaining, from the management server, the end time of the update prohibitive attribute given to the data on which the request is made, a step of judging whether or not the end time of the update prohibitive attribute has passed, and a step of sending, when it is judged that the end time of the update prohibitive attribute given to the data on which the request is made has passed, permission to change the update prohibitive attribute given to the data on which the request is made to the storage system.