According to one embodiment, an X-ray computed tomography apparatus comprises a forward projection unit, a filter process unit, a calculation unit, and an update process unit. The forward projection unit exerts a forward projection of an image, the image being generated from first projection data acquired by a scanning or an updated image, and to generate second projection data corresponding to at least one ray direction. The filter process unit exerts a filter process to the second projection data corresponding to the at least one ray direction using at least one angularly variant low pass filter. The calculation unit calculates a subtraction between the first projection data and the second projection data after the filter process. The update process unit updates the image using the subtraction result.
