An imaging device including: a photoelectric converter including first and second electrodes and a photoelectric conversion layer therebetween; a voltage supplier; an output circuit for outputting a signal corresponding to the potential of the second electrode; and a detector for detecting the signal level. The change rate of the conversion efficiency of the photoelectric converter with respect to a bias voltage applied between the electrodes when the bias voltage is in a first range is greater than that when the bias voltage is in a second range higher than the first range. The voltage supplier, when the detected level is a first threshold or higher, causes the potential difference between the electrodes to be a first difference, and, when the detected level is lower than a second threshold that is the first threshold or lower, causes the potential difference to be a second difference greater than the first difference.