1. A device for image reconstruction at different X-ray energies, comprising: an X-ray source that irradiates a specimen to be imaged with X-rays; an energy-dispersive detector that detects a characteristic X-ray emitted from the specimen to be imaged; a signal processor that quantifies the peak of the characteristic X-ray detected by the detector; and an image reconstruction device that reconstructs an image on the basis of a signal from the signal processor.