An X-ray CT apparatus has an irradiation unit, a determination unit, and a displaying unit. The irradiation unit is configured to emit an X-ray. The determination unit determines a tube current value modulation to extend to a body axis direction in a predetermined rotation angle of the irradiation unit based on an index value to show a dispersion of CT values in a required area in a reconstructed image, and a scan condition. The displaying unit displays an image of the index value and an image of the tube current value modulation on an image used for positioning and aligns the image along the body axis direction on the image used for positioning.