Provided is a radiation image detector including an internal power supply section, which is capable of being charged, wherein signals of radiographed image data and the like can be prevented from being influenced by noise even when the internal power supply section is charged by power supplied from an external power source.The radiation image detector includes a battery (28) to supply power to each section, an external power supply terminal (27) to receive power from an external power source (PW) so as to allow the battery (28) to be charged, and a cassette control section (30) to control supply of the power to the battery (28), the power being received from the external power source (PW) via the external power supply terminal (27). When detecting that the external power supply terminal (27) receives power from the external power source (PW), the cassette control section (30) judges an operating state of each section, and controls the supply of the power to the battery (28) according to the operating state of each section, the power being received from the external power source (PW) via the external power supply terminal (27).
