To provide a method of refresh operation for a flat panel radiation imager that makes it possible to carry out a refresh operation in such a way that electric charge that is accumulated in pixels by photoelectric conversion is efficiently released with low power consumption and during a short period of time. Control signals of the refresh operation are turned into a plurality of successive pulses at regular intervals; and timing is adjusted in a way that adjacent switching elements disposed on the same signal line are not turned ON at the same timing.