Operating device for a screen, such as a window covering, which screen is provided with a screen shaft, said operating device comprising: a drive element (60; 60') for the screen shaft, - a first operating mechanism comprising a first operating element which is connected to a first movement transfer element connected by means of a first transmission to the drive element, wherein the first operating mechanism is configured to convert a linear movement of the first operating element to a rotational movement of the drive element for operating the screen shaft in a first rotational direction, - a second operating mechanism comprising a second operating element which is connected to a second movement transfer element connected by means of a second transmission to the drive element, wherein the second operating mechanism is configured to convert a linear movement of the second operating element to a rotational movement of the drive element for operating the screen shaft in a second rotational direction opposite to the first rotational direction, wherein the first transmission is provided with a first unidirectional coupling and a first toothed wheel (33; 63) on the drive element for co-action with the first unidirectional coupling in an operational position, wherein the second transmission is provided with a second unidirectional coupling and a second toothed wheel (43; 63) on the drive element for co-action with the second unidirectional coupling in an operational position, wherein the first transmission is further provided with a first activator for activating the operational position of the first unidirectional coupling, wherein the first movement transfer element is connected to the first activator, and wherein the second transmission is further provided with a second activator for activating the operational position of the second unidirectional coupling, wherein the second movement transfer element is connected to the second activator, characterized in that the first unidirectional coupling is provided with a central first body with a first opening and a number of flexible first arms and the second unidirectional coupling is provided with a central second body with a second opening and a number of flexible second arms, wherein the first activator is provided with a first flange with a number of first protrusions for bending the first arms outward in radial direction of the first unidirectional coupling and that the second activator is provided with a second flange with a number of second protrusions for bending the second arms outward in radial direction of the second unidirectional coupling. - a first operating mechanism comprising a first operating element which is connected to a first movement transfer element connected by means of a first transmission to the drive element, wherein the first operating mechanism is configured to convert a linear movement of the first operating element to a rotational movement of the drive element for operating the screen shaft in a first rotational direction, - a second operating mechanism comprising a second operating element which is connected to a second movement transfer element connected by means of a second transmission to the drive element, wherein the second operating mechanism is configured to convert a linear movement of the second operating element to a rotational movement of the drive element for operating the screen shaft in a second rotational direction opposite to the first rotational direction, wherein the first transmission is provided with a first unidirectional coupling and a first toothed wheel (33; 63) on the drive element for co-action with the first unidirectional coupling in an operational position, wherein the second transmission is provided with a second unidirectional coupling and a second toothed wheel (43; 63) on the drive element for co-action with the second unidirectional coupling in an operational position, wherein the first transmission is further provided with a first activator for activating the operational position of the first unidirectional coupling, wherein the first movement transfer element is connected to the first activator, and wherein the second transmission is further provided with a second activator for activating the operational position of the second unidirectional coupling, wherein the second movement transfer element is connected to the second activator, characterized in that the first unidirectional coupling is provided with a central first body with a first opening and a number of flexible first arms and the second unidirectional coupling is provided with a central second body with a second opening and a number of flexible second arms,