A photoelectric conversion device includes a photoelectric conversion unit configured to output a photon detection signal in response to an incidence of a photon, a counting unit configured to count the photon detection signal output from the photoelectric conversion unit, and a counting control unit configured to control a counting operation in the counting unit. The counting control unit is configured to reset a count value and restart the counting operation from an initial value, when a count value from a start of the counting operation to a first time is less than a first threshold value and a count value from the start of the counting operation to a second time after the first time is equal to or greater than a second threshold value greater than the first threshold value.