Provided is a virtual-machine managing device including: a model acquiring unit that acquires, for each server device, a performance model indicative of plural correspondent relationships between a workload amount and performance information on a workload; a performance-information acquiring unit that acquires the performance information on a virtual machine to be moved running on a current server device; a conversion unit that converts the performance information on the virtual machine to be moved into a combination of the workload amount and the workload characteristic value concerning the virtual machine to be moved, by using the performance model of the current server device; and an estimating unit that estimates performance information on the virtual machine to be moved on a destination server device serving as a candidate for a destination of movement of the virtual machine to be moved, by applying the combination converted by the conversion unit to the performance model of the destination server device.