According to one embodiment, an X-ray CT apparatus includes an generation unit, detection unit, processing unit, and reconstruction unit. The generation unit irradiates an object with X-rays. The detection unit includes detection elements corresponding to a plurality of channels, which output detection signals upon detecting X-rays. The processing unit smoothes projection data constituted by numerical values corresponding to signals output from the elements so as to more strongly smooth a portion exhibiting a larger amount of change in the numerical value. The reconstruction unit reconstructs an image by using a plurality of projection data smoothed by the image processing unit.
