there is provided a data migrating method including the steps of : calculating , in a case where data stored in a volume is migrated to another volume , a required period of time for migrating the data based on a size of data to be migrated and volume configuration information on the volume in which the migrated data is stored and the volume to which the data is to be migrated ; determining a start time at which the data migration starts to generate a volume migration plan ; setting a priority of the generated volume migration plan ; prioritizing , in a case where a periods of time during which the generated volume migration plan is executed and a period of time during which an existing volume migration plan is executed are overlapped with each other , and changing the start time of at least one of those volume migration plans having a lower priority .