Upon input of a synchronization signal, which indicates a start of an X-ray emission, from a source control unit for controlling an X-ray source, an electronic cassette makes an FPD start an accumulation operation and measurement of an X-ray dose. The electronic cassette and a console command their communicators to stop communication of any signal other than a stop signal, which stops the X-ray emission from the X-ray source, during the accumulation operation of the FPD. As soon as the X-ray dose has reached a predetermined threshold value, the electronic cassette transmits the stop signal to the source control unit through the console. A delay in transmission of the stop signal due to communication congestion or signal collision does not occur, because the electronic cassette and the console stop the communication of the signal other than the stop signal.