An optical operational memory device comprises a light-emitting device, a first and second phototransistors, and a load resistor. The light-emitting device and the first phototransistor are connected electrically in series to form an optical bistable switch based on optical positive feedback. The second phototransistor is connected in parallel to the optical bistable switch, and the load resistor is connected in series to the optical bistable switch. The time constant given by the product of the current gain of the second phototransistor, the base-collector capacitance of the second phototransistor, and the resistance of the load resistor is larger than the period required for recombination of the excess majority carriers in the base of the first phototransistor. A single optical beam modulated with pulse signals is input to the first and the second phototransistors simultaneously. The optical pulse with a peak power in a predetermined range turns the optical bistable switch on, and the pulse with higher peak power turns the optical bistable switch off.