Abstract: The present invention relates to a brake-power transmission device, especially for motor vehicles, including an actuated input member, an output member to exert a boosting force, especially on a main brake cylinder, and a control valve arranged in a control housing to regulate the boosting force. An axially movable pressure piece is provided in the area of a reaction member. The pressure piece is supported on the input member or the control housing, thereby permitting changes to be made in the power transmission ratio. There is a general need to provide a brake-power transmission device that enables increased boosting only when required and that allows for mechanical sensing of the brake actuation speed so that immediate maximum boost force can be exerted when required without any time delay.