According to one embodiment, a radiation diagnostic apparatus includes a photon-counting detector, a counting information storage unit, an image reconstituting unit, and a controlling unit. The detector performs counting on light derived from incident radiation. The counting information storage unit stores therein counting information based on the counting result of the detector. The image reconstituting unit reconstitutes a medical image by performing a back projection process on projection data that is generated by use of the counting information stored in the counting information storage unit. After the reconstitution of the medical image, the controlling unit performs control so that all or part of the counting information is maintained in the counting information storage unit.