An electronic cassette for radiographic imaging includes a radiation imaging detector for detecting X-rays from an object and creating an X-ray image of the object. A battery supplies the radiation imaging detector with power. A power receiver wirelessly receives power from a wireless power transmission apparatus for charging the battery. A housing is formed from an electrical conductor, for containing the radiation imaging detector and the power receiver. A path opening is formed in the housing, and disposed between the power receiver and the wireless power transmission apparatus. A cover device is formed from a material having electrical insulating property and thermal conductivity, for closing the path opening, and conducting heat of the power receiver to the housing for dissipation. Preferably, the cover device contains synthetic resin. Also, a profile line of the path opening is at least partially curved.