An X-ray CT apparatus includes: intensity distribution data acquiring circuitry is configured to acquire, by performing a first scan, intensity distribution data of X-rays being radiated from an X-ray tube and having passed through a subject scan controlling circuitry is configured to estimate an X-ray dose with which it is possible to discriminate individual X-ray photons having passed through the subject based on the intensity distribution data and to cause a second scan that is for a photon counting CT purpose to be performed by causing the estimated dose of X-rays to be radiated from the X-ray tube to the subject a counting result acquiring circuitry is configured to acquire, by the second scan, a counting result by counting the X-ray photons being radiated from the X-ray tube and having passed through the subject and an image reconstructing circuitry is configured to reconstruct X-ray CT image data based on the counting result.
