A medical imaging apparatus includes a reconstruction unit, a ROI setting unit, and a controller. The reconstruction unit receives projection data that is based on radiation detected by a detector, divides the projection data into a plurality of subsets, and apply a reconstruction process to the subsets by successive approximation to successively generate images. The ROI setting unit sets a ROI in the images. The controller obtains a variation value indicating a change in image quality from the images, and, when the variation value reaches a predetermined value, instructs the reconstruction unit on a new subset count less than the number of the subsets to sequentially reconstruct subsets as many as the new subset count into an image. The reconstruction unit assigns a weight to the projection data based on the ROI, and divides the projection data into the subsets based on the weight.