A key structure includes a casing, a restoring member and a keycap assembly. The casing has an opening. The restoring member is disposed in the casing. The keycap assembly includes a keycap and a holder. The keycap includes a pressing portion and a central shaft. The pressing portion has a bottom surface. The central shaft connects to the bottom surface. The central shaft has a hemispherical portion adjacent to the bottom surface. The holder is inserted into the casing via the opening and contacts the restoring member. The holder includes a shaft bore. The shaft bore has an arcuate socket. The central shaft passes through the shaft bore and contacts the restoring member, and the hemispherical portion is accommodated in the arcuate socket.