Provided is a method of controlling a virtual computer system in which a physical computer includes a plurality of physical CPUs that is switchable between a sleep state and a normal state, and a virtualization control unit divides the physical computer into a plurality of logical partitions to run a guest OS in each of the logical partitions and controls allocation of resources of the physical computer to the logical partitions, causes the virtualization control unit to: receive an operation instruction for operating the logical partitions; and if the operation instruction is for deleting a virtual CPU from one of the logical partitions, delete this virtual CPU from a table for managing virtual CPU-physical CPU allocation and put, if the deleting leaves no virtual CPUs allocated to one of the physical CPUs that has been allocated the deleted virtual CPU, this one of the physical CPUs into the sleep state.