1. An enclosure inspection method, comprising: radiating X-rays from the exterior of an inspection object to image the inspection object; determining whether a suspected object is enclosed as an enclosure in the inspection object from the obtained X-ray image; radiating a terahertz wave or a millimeter wave to the suspected object from the exterior of the inspection object in which the suspected object is enclosed; and determining whether the suspected object is a predetermined object by detecting a scattered wave, a transmitted wave, or a reflected wave of the terahertz wave or millimeter wave.