An FPD is provided with an ammeter for measuring current on a wired connection of a bias line that applies a bias voltage to pixels. A control circuit compares the measured value of the ammeter and a threshold value. When the measured value of the ammeter is equal to or larger than the threshold value, the control circuit judges that an emission of X-rays from an X-ray source is started. Until before the start of the X-ray irradiation is detected, the control circuit stops supplying electric power to a signal processing circuit, and turns on all TFTs. Once the start of the X-ray irradiation is detected, the control circuit turns off all the TFTs, and makes the FPD shift to a charge accumulation operation. Thereafter, the control circuit turns on a processing power source to start supplying the electric power to the signal processing circuit.