The interrupt level storing unit (16) stores one or more interrupt levels indicating the priority of a generated interrupt and stores the interrupt level having the highest priority among the stored interrupt levels as a second interrupt mask level. The second interrupt type determination unit (13) sets an interrupt level corresponding to the interrupt type of a newly generated interrupt. The priority determination unit (14) notifies the interrupt to the virtual machine control unit (20) when the interrupt level of the newly generated interrupt is higher than the stored second interrupt mask level. As a result, the priority of the virtual machine can be determined according to the task priority and the switching of virtual machines can be adequately controlled even if the virtual machines cannot notify the task priority.