An optical element including a plurality of reference members formed on a first side surface, and a method and apparatus for fixedly joining the optical element with the first side surface facing down. When the IP telephony system determines that this situation is occurring, the IP telephony system acts to connect the two parties, rather than have both of them see their new call setup attempt fail because the other party’s telephony device is indicated to be busy. A database is stored in the electronic control unit. Main roads, spur roads, and snig tracks are constructed in the logging area. The computer case includes a positioning portion protruding from a surface of the computer case and having a connecting surface, and an interface card fastener mounted on the surface of the computer case and having a pressing surface pressing the extension piece of the interface card against the connecting surface.