According to one embodiment, an X-ray computed tomography apparatus includes an X-ray tube, an X-ray detector, preprocessing circuitry, a reconstruction processor and control circuitry. The X-ray detector configured to detect X-rays generated from the X-ray tube. The preprocessing circuitry configured to generate projection data by executing preprocessing for data acquired by the X-ray detector, based on a preprocessing condition. The reconstruction processor configured to generate image data by executing reconstruction processing for the projection data based on a reconstruction condition. The control circuitry configured to cause a storage to store the projection data in association with the preprocessing condition and read out, based on a designated preprocessing condition.
