According to one embodiment, an apparatus includes a reconstructing unit, a first control unit, a detecting unit, a generating unit, and a second control unit. The first control unit controls the reconstructing unit to reconstruct first images based on projection data collected in first periods. The detecting unit detects second periods which belong to pulsation cycles different from one another and in which an organ to be imaged is in the substantially same form, based on the first images. The generating unit generates data for reconstruction including projection data for the required angle range by combining projection data collected in third periods close to the second periods. The second control unit controls the reconstructing unit to reconstruct a second image based the data for reconstruction.