An object of the invention is to provide a storage controller and control method that can efficiently and easily prevent reduced data I/O processing performance due to an imbalance between loads on controllers. In the storage controller and control method for providing, to a host computer, logical volumes created in a storage area provided by a storage device and controlling data I/O to/from the logical volumes, the state of loads on the control units for controlling data I/O to/from the logical volumes is monitored, and a control unit allocated to a logical volume is changed to another control unit to equalize loads on the control units.