A computer system having a plurality of controllers for data input/output control is provided, wherein even if a control authority of a processor is transferred to another processor and the computer system migrates control information necessary for a controller to execute data input/output processing, from a shared memory to a local memory for the relevant controller, the computer system prevents the occurrence of unbalanced allocation of a control function necessary for data input/output control between the plurality of controllers; and a load equalization method for such a computer system is also provided.