A lens apparatus for mounting on a camera main body including an image-pickup element, comprising: a focus lens means which is movable in an optical axis direction for focusing; a zoom lens means which is movable in the optical axis direction for zooming; a zoom detector for detecting a zoom value of the zoom lens means; an aperture-stop device in which an aperture which can change in size to adjust a light quantity; a stop-value detector for detecting a stop value of the aperture-stop device; a splitting optical means disposed between the aperture-stop device and the image-pickup element; a focus-condition detection means for detecting a focus condition based on light from the splitting optical means; an actuator for driving the focus lens means in the optical axis direction; a controller for controlling the actuator based on an output from the focus-condition detection means; and a manual operation member for moving the focus lens means in the optical axis direction by a manual operation, wherein: the controller is configured to obtain an F-number of the lens apparatus based on an output from the zoom detector and an output from the stop-value detector, characterized in that when the F-number, adjustable by the stop value of the aperture stop device, exceeds a predetermined value, the controller causes operation of the actuator to be stopped by switching from an autofocus condition in which the focus lens means is driven by the actuator automatically to a manual focus condition in which the focus lens means can be driven by the manual operation member and when the F-number is less than or equal to the predetermined value, the controller causes the operation of the actuator to be continued in an autofocus condition in which the focus lens means is driven by the actuator automatically. a focus lens means which is movable in an optical axis direction for focusing; a zoom lens means which is movable in the optical axis direction for zooming; a zoom detector for detecting a zoom value of the zoom lens means; an aperture-stop device in which an aperture which can change in size to adjust a light quantity; a stop-value detector for detecting a stop value of the aperture-stop device; a splitting optical means disposed between the aperture-stop device and the image-pickup element; a focus-condition detection means for detecting a focus condition based on light from the splitting optical means; an actuator for driving the focus lens means in the optical axis direction; a controller for controlling the actuator based on an output from the focus-condition detection means; and a manual operation member for moving the focus lens means in the optical axis direction by a manual operation, wherein: the controller is configured to obtain an F-number of the lens apparatus based on an output from the zoom detector and an output from the stop-value detector, characterized in that when the F-number, adjustable by the stop value of the aperture stop device, exceeds a predetermined value, the controller causes operation of the actuator to be stopped by switching from an autofocus condition in which the focus lens means is driven by the actuator automatically to a manual focus condition in which the focus lens means can be driven by the manual operation member and when the F-number is less than or equal to the predetermined value, the controller causes the operation of the actuator to be continued in an autofocus condition in which the focus lens means is driven by the actuator automatically. the controller is configured to obtain an F-number of the lens apparatus based on an output from the zoom detector and an output from the stop-value detector, characterized in that when the F-number, adjustable by the stop value of the aperture stop device, exceeds a predetermined value, the controller causes operation of the actuator to be stopped by switching from an autofocus condition in which the focus lens means is driven by the actuator automatically to a manual focus condition in which the focus lens means can be driven by the manual operation member and when the F-number is less than or equal to the predetermined value, the controller causes the operation of the actuator to be continued in an autofocus condition in which the focus lens means is driven by the actuator automatically.