A user terminal device (100, 200), comprising: a hinge configured to enable the user terminal device (100, 200) to be foldable; a single flexible display (110, 230) configured to be divided into a first area and a second area by the hinge, wherein an exposure area (340, 2310, 2330) of the second area is not covered by the first area when the user terminal device (100, 200) is folded so that a part of the first area touches a part of the second area; a detector configured to detect a user interaction; and a controller (130, 290) configured to, in response to detecting a folding of the single flexible display (110, 230) along a folding line, control the single flexible display (110, 230) to display a predetermined user interface, UI, on the exposure area (340, 2310, 2330), wherein the controller (130, 290) is further configured to, control the single flexible display (110, 230) to display a UI (610, 620, 630, 640, 1210) for releasing a lock state of the user terminal device (100, 200) on the exposure area as the single flexible display (110, 230) is in a folded state, in response to detecting an unfolding of the single flexible display (110, 230) after a lock release command is input through the UI for releasing the lock state of the user terminal device (100, 200), control the single flexible display (110, 230) to display a home screen, and in response to detecting an unfolding of the single flexible display (110, 230) while the lock release command is not input through the UI for releasing the lock state of the user terminal device (100, 200), control the single flexible display (110, 230) to display a UI for releasing the lock state of the user terminal device (100, 200) on full screen. a hinge configured to enable the user terminal device (100, 200) to be foldable; a single flexible display (110, 230) configured to be divided into a first area and a second area by the hinge, wherein an exposure area (340, 2310, 2330) of the second area is not covered by the first area when the user terminal device (100, 200) is folded so that a part of the first area touches a part of the second area; a detector configured to detect a user interaction; and a controller (130, 290) configured to, in response to detecting a folding of the single flexible display (110, 230) along a folding line, control the single flexible display (110, 230) to display a predetermined user interface, UI, on the exposure area (340, 2310, 2330), wherein the controller (130, 290) is further configured to, control the single flexible display (110, 230) to display a UI (610, 620, 630, 640, 1210) for releasing a lock state of the user terminal device (100, 200) on the exposure area as the single flexible display (110, 230) is in a folded state, in response to detecting an unfolding of the single flexible display (110, 230) after a lock release command is input through the UI for releasing the lock state of the user terminal device (100, 200), control the single flexible display (110, 230) to display a home screen, and in response to detecting an unfolding of the single flexible display (110, 230) while the lock release command is not input through the UI for releasing the lock state of the user terminal device (100, 200), control the single flexible display (110, 230) to display a UI for releasing the lock state of the user terminal device (100, 200) on full screen.