Abstract: To preclude a rolling diaphragm forming together with a metallic diaphragm plate the movable wall of a vacuum brake force booster from being detached from a groove accommodating the radially inward area of the rolling diaphragm, it is provided, in the practice of the invention, that the contour of a supporting face for the diaphragm plate formed on the control valve housing and the contour of the radially inward area (sealing bead of the rolling diaphragm correspond to the curved shaped of the radially inward area (curvature) of the diaphragm plate, and that both the contour of the supporting face and the one of the radially inward area (sealing bead) of the rolling diaphragm correspond to the curved shape of the radially inward area (curvature) of the diaphragm plate, and that the groove with the axial dimension thereof extends into the bearing area of the diaphragm plate of the support face.