A brake booster having a brake valve disposed inside a booster piston, the brake valve comprises a valve bushing including a valve seat and a slide that is pressed by a spring against the valve seat of the valve bushing. The slide is supported with play at a great distance from the valve seat, so that it can be pivoted slightly around the vicinity of its bearing. The pivotability of the slide facilitates its centering in the valve seat, so that the valve closes dependably even in the presence of bearing tolerances or valve seat tolerances. Seals required for sealing off the slide have an elastic behavior, and are disposed in the vicinity of the bearing. As a result, reliable sealing is assured despite the pivotability of the slide.