The vehicle brake-specific diaphragm of the invention includes a vessel-form member and a flange portion formed at a peripheral edge of an opening in the vessel-form member, wherein the vessel-form member and the flange portion are each formed of a rubber body including silicone rubber and a substrate fabric embedded in the rubber body, the substrate fabric including aramid short fibers or polyester fibers, and having a thickness of 0.25 mm or more. Accordingly, the inventive diaphragm does not only have durability during operation in both the high-temperature and the normal-temperature area but also exerts much better durability during operation in the low-temperature area.