A mobile terminal device and methods are disclosed. A display module is provided on a first surface of the casing. A first detection module is provided to cover the display module and detects a user's operation. A second detection module is provided on a second surface opposed to the first surface and detects a user's operation. A lock control module sets a lock function for preventing the user's wrong operation. The lock control module releases the setting of the lock function, if the lock function is set and if the first detection module has detected a first operation. The lock control module releases the setting of the lock function, if the lock function is set and if the second detection module has detected a second operation.