The present invention provides a dome diaphragm having high strength wholly and uniformly while maintaining a small thickness of a dome portion. A diaphragm 1 according to the present invention is a dome diaphragm including a dome portion 2. The dome portion 2 is divided into a plurality of small portions 4, and a ridge portion 7 is formed at a boundary of the small portions 4. In accordance with this configuration, the ridge portions 7 exist over the entire dome portion 2, and the ridge portions 7 can serve as frames for reinforcing the dome portion 2.