An automatic focusing device comprises a detector for detecting distributions of the images of an object which are formed by two light beams passing through two different points in a photographing optical system and for providing corresponding video signals. The video signals are processed to obtain an output signal representative of a relative positional relation between the video signals for use in establishing the optical system moving direction and the distance of movement of the focusing position, or to determine only the direction of movement of the optical system so that the optical system is moved in the direction thus determined to the focusing position. The automatic focusing operation can be accomplished without using movable members other than the photographing lens of the optical system, or in the case of using a movable member, the focusing operation can be achieved with high accuracy by operating the movable member only once.