Proposed are a storage system and a data migration method capable of effectively performing data migration between storage apparatuses. This storage system includes a host apparatus equipped with a function for copying data stored in a first volume of a first storage apparatus in file units to a corresponding second volume of a second storage apparatus, and a controller equipped with a function for controlling the first and second storage apparatuses to copy data stored in the first volume to the second volume in volume units. Necessary control processing is executed to decide whether to migrate data stored in the first volume in volume units or file units according to the status of data stored in the first volume to be subject to data migration.