An information processing system that maintains balance in the processing loads between processors and that includes operating systems, which each perform execution control on processing tasks by assigning each task to a task group and causing all tasks in the same task group to be executed on the same processor, and a hypervisor that associates each processor with one or more task groups in the operating systems and causes each operating system to perform the execution control so that all tasks in the same task group are executed on the processor associated with the same task group. The hypervisor sequentially acquires load indicators indicating a processing load of each task group in each operating system, refers to the processing loads indicated by the sequentially acquired load indicators, and when determining that the processing loads are not balanced between the processors, re-associates the processors with the task groups.