According to one embodiment, a radiation detector includes a detecting part, and a transmitting part. The detecting part is configured to output a signal. The signal corresponds to radiation incident on the detecting part. The transmitting part includes a first conductive layer, a second conductive layer, and an organic layer. The first conductive layer is electrically connected with the detecting part, and is configured to transmit the signal. The second conductive layer is separated from the first conductive layer. At least a portion of the organic layer is between the first conductive layer and the second conductive layer.