An exchangeable lens includes a lens system which forms an image of a target object on which the lens system is focused, a focus adjusting means manually operable for adjusting the focus of the lens system, a direction signal generating means which generates a direction signal representing the relationship between the operational direction of the focus adjusting means of the lens and change of the camera-to-object distance to be focused on by the lens system and a transmitting means which transmits the signal to a camera on which the exchangeable lens is detachably mounted. The camera includes a focus detecting means which receives a light coming from an object and passing through the lens system, a focus condition determining means which is responsive to the output of the focus detecting means to determine the focus condition and the direction of operation of the focus adjusting means to attain an in-focus condition for the focus adjustment and a display means which indicates the focus condition and the direction of focus adjustment. The display means indicates a proper direction of operation of the focus adjusting means towards an in-focus condition, even if the relationship between the operational direction and change of focus differs with the exchangeable lenses.