According to one embodiment, a radiation image diagnostic apparatus includes a gantry and image reconstruction circuitry. The gantry images a subject with radiation over a plurality of phases and acquires a plurality of imaging data sets for the plurality of phases. The image reconstruction circuitry executes an iterative reconstruction for the plurality of imaging data set to generate a plurality of reconstruction images for the plurality of phases. The image reconstruction circuitry executes the iterative reconstruction using, as the initial image, the first reconstruction image obtained by executing the iterative reconstruction based on the imaging data set of the first phase, generating a second reconstruction image for the second phase different from the first phase.
