Provided is a photon counting CT device for estimating an exposure dose to a subject, precisely in a simple configuration, irrespective of a spectrum shape of X-rays being applied. An exposure dose derived from the X-rays with predetermined intensity is obtained in every energy range provided in advance, and held as exposure per band data. When an imaging condition is provided, X-rays are applied in accordance with the imaging condition thus provided, and a photon count (intensity) of the incident X-rays as to each energy range is obtained, in the shape of spectrum of the X-rays applied to a detector without placing the subject. The intensity of the incident X-rays is multiplied by the exposure per band, and the results as to all the energy ranges are added up. Accordingly, the exposure dose caused by the X-rays being applied in accordance with the provided imaging condition is estimated.
