An information terminal incorporating a function of a mobile phone is provided in which a subscriber ID card used in a GSM system or the like is prevented from being stolen. When a key is inserted in the key hole of a cylinder lock and turned by 90 degrees, the cam plate is turned to rotate a lever of the rotation arresting shaft through a coupling rod plate, and the arresting part is turned by 90 degrees in a lock part of a groove at the back side of a slide lock device. As a result, the slide lock device is prevented from sliding, and the arrested part is kept arrested by the arresting part. Therefore, a back lid cannot be opened, and the cam plate locks a power source lever, so that a power switch cannot be turned on.