A photoelectric conversion device includes a photoelectric conversion region, a readout circuit, and a counting circuit. The photoelectric conversion region is configured to generate a signal charge. The readout circuit is configured to, when reading out a signal that is based on the signal charge generated at the photoelectric conversion region, selectively perform first readout for reading out the signal using avalanche multiplication that is based on the signal charge and second readout for reading out the signal without causing avalanche multiplication to occur with respect to at least a part of the signal charge. The counting circuit is configured to count a number of occurrences of avalanche current which is caused to occur by avalanche multiplication in the first readout.