A screen door operating device for automatically opening and closing a screen door, the screen door comprising an elongate insect screen holder for a rolled or concertina folded insect screen that with an edge is attached to an elongate, movable and in operation vertically oriented closing strip which is parallel to the elongate insect screen holder and is movable between an open position in which the insect screen is rolled up or folded and a closed position in which the insect screen is unrolled or unfolded, which screen door operating device comprises: - an upper guide profile, for guiding the upper end of the movable vertical closing strip, which upper guide profile can be connected with a first end to the insect screen holder, as well as - a lower guide profile, for guiding the lower end of the movable vertical closing strip, which lower guide profile can be connected with a first end to the insect screen holder, - an upper driver which is movable in the upper guide profile and which can be coupled to the upper end of the vertical closing strip, - a lower driver which is movable in the lower guide profile and which can be coupled to the lower end of the vertical closing strip, - a drive for moving the drivers (9, 11) and thus also the closing strip, for automatically opening and closing the screen door, which drive can be mounted against the insect screen holder and is present in the lower and upper guide profile (5, 7), and - at least one switch for operating the drive, wherein the drive comprises: - an elongate, flexible, upper drive element, to which the upper driver is attached, as well as - an elongated, flexible, lower drive element to which the lower driver is attached, and - a drive motor mountable against the insect screen holder, which drive elements (21, 27) are connected to the drive motor in such a way that they move the two drivers (9, 11) simultaneously in the guide profiles (5, 7) during opening and closing of the screen door, characterized in that the drive further comprises a middle drive element which is wrapped around a drive wheel connected to the drive motor, from which drive wheel two parallel branches (17A, 17B) of the middle drive element extend, wherein the upper and lower drive elements (21, 27) with their ends are attached to both branches (17A, 17B) of the middle drive element. - an upper guide profile, for guiding the upper end of the movable vertical closing strip, which upper guide profile can be connected with a first end to the insect screen holder, as well as - a lower guide profile, for guiding the lower end of the movable vertical closing strip, which lower guide profile can be connected with a first end to the insect screen holder, - an upper driver which is movable in the upper guide profile and which can be coupled to the upper end of the vertical closing strip, - a lower driver which is movable in the lower guide profile and which can be coupled to the lower end of the vertical closing strip, - a drive for moving the drivers (9, 11) and thus also the closing strip, for automatically opening and closing the screen door, which drive can be mounted against the insect screen holder and is present in the lower and upper guide profile (5, 7), and - at least one switch for operating the drive, wherein the drive comprises: - an elongate, flexible, upper drive element, to which the upper driver is attached, as well as - an elongated, flexible, lower drive element to which the lower driver is attached, and - a drive motor mountable against the insect screen holder, - an elongate, flexible, upper drive element, to which the upper driver is attached, as well as - an elongated, flexible, lower drive element to which the lower driver is attached, and - a drive motor mountable against the insect screen holder, which drive elements (21, 27) are connected to the drive motor in such a way that they move the two drivers (9, 11) simultaneously in the guide profiles (5, 7) during opening and closing of the screen door, characterized in that the drive further comprises a middle drive element which is wrapped around a drive wheel connected to the drive motor, from which drive wheel two parallel branches (17A, 17B) of the middle drive element extend, wherein the upper and lower drive elements (21, 27) with their ends are attached to both branches (17A, 17B) of the middle drive element.