According to an embodiment, detector cells are provided on a substrate, divided into groups, and detect an X-rays. Switches respectively connected to the detector cells. The data acquisition elements are respectively connected to the groups and configured to integrate electrical signals from a detector cells belonging to each of the groups. The control circuitry are configured to control the switches for each of the groups so as to switch between first connection for substantially simultaneously reading out electrical signals from a detector cells belonging to each of the groups and second connection for reading out electrical signals from a detector cells belonging to each of the groups at different timings.