A radiation detector according to an embodiment includes a sensor, an electronic circuitry, a switch, and a control circuitry. The sensor configured to be formed of plural electrodes and detect radiation. Based on signals output from the electrodes, the electronic circuitry configured to output digital data. The switch configured to be provided between each of the electrodes and the electronic circuitry. The control circuitry configured to control the switch, based on a positional relation between the plural electrodes and an anti-scatter grid.