A numerical control device is for machining a machining object by moving a tool and the machining object relative to each other along a movement path while applying vibration, by use of a drive axis provided for the tool or the machining object. The device includes a storage unit that holds an invalid frequency region, and a vibration condition determining unit to determine a frequency for the vibration, based on a rotational speed of a main shaft for rotating the machining object, a number of vibrations of the vibration in each one rotation of the main shaft, and the invalid frequency region.