In scheduling shared processing that has a higher priority than LPAR processing, giving precedence to physical CPUs running idle LPARs prevents prolonged hold-up of LPAR processing. In a system is comprised of multiple physical CPUs, multiple LPARs to which these physical CPUs are allocated and which execute programs under their guest OSes, and a management program managing these LPARs, a few additional units are introduced: a guest OS monitoring unit that can grasp the states of guest OSes running on these LPARs and a dispatcher unit that allocates one of these physical CPUs to shared processing requested by the management program, which has a higher priority than LPAR processing. When a request for shared processing arises, the dispatcher unit interrogates the guest OS monitoring unit and, based on the information obtained from it, gives priority of allocation to the physical CPU processing an idle LPAR.