An automatic fluid-powered toothbrush provided with a fluid vibrator motor having a power chamber with a movable wall such as a piston or a membrane connected to the brush member for causing vibrating movement thereof. At least one fluid port is arranged in the fluid path, and a valve is arranged with each port for opening and closing same. The closed or opened condition of each valve is determined by a bistable fluid switch controlled by the fluid pressure in the power chamber. The fluid switch may have a movable switching component which acts as a valve body. An auxiliary chamber is preferably provided in constant fluid communication with the fluid supply aperture and also has a movable wall. The movable walls of the power chamber and the auxiliary chambers are coupled to one another for the transmission of movement to one another. The chambers and passages may be arranged in a plurality of plates, such as, of a plastic, which are stacked with rubber packing plates between them, parts of which may act as a diaphragm-type movable wall or as a valve body.