The invention relates to a flap drive system for a flap which is movably mounted on a furniture carcass. The flap drive system is arranged on a sidewall of the furniture carcass. The flap drive system includes a mechanical actuating unit having an actuating arm that can be connected to the flap and an accumulator acting upon the actuating arm, and an electric drive, fastened on the mechanical actuating unit for driving the flap. The electric drive has at least one electric motor, and a gear stage which allows the transmission of force from the electric drive onto the mechanical actuating unit. The gear stage is designed as a separate component, and has a housing that is independent from the mechanical actuating unit and the electric drive or an independent mounting plate.