A radiation detector includes a memory controller and a sleep control unit. The sleep control unit supplies a power supply power to a main control unit and cuts off supply of the power supply power to at least a part other than the main control unit in a first power consumption reduction mode. In addition, the sleep control unit cuts off supply of the power supply power to at least a part of the main control unit and at least a part other than the main control unit in a second power consumption reduction mode. In addition, the memory controller prevents a volatile memory from being deactivated during the second power consumption reduction mode.