A user terminal device, comprising: a display configured to be divided into a first area and a second area which is larger than the first area with reference to a folding line; a cover disposed on a rear side of the display; a folding detector configured to detect the display being folded; detector configured to detect a user interaction on the display and the cover; and a controller configured to: in response to the folding detector detecting the display being folded along the folding line such that the first area and the second area face each other, control the detector to detect a user interaction through an exposure area, which is an exposed part of the second area, and the cover, and in response to the folding detector detecting the display being folded along the folding line such that two parts of the cover face each other, control the detector to detect a user interaction through the first area and the second area, wherein the controller is further configured to, in response to a telephone call request being received while the display is folded such that the first area and the second area face each other, control the display to display a UI for informing that a telephone call request is received on the exposure area (340, 2703, 2707), and accept or reject the telephone call request according to a user interaction (2705, 2711) detected on the cover (2509, 2701, 2709), wherein the user interaction is a dragging gesture or a flicking gesture. a display configured to be divided into a first area and a second area which is larger than the first area with reference to a folding line; a cover disposed on a rear side of the display; a folding detector configured to detect the display being folded; detector configured to detect a user interaction on the display and the cover; and a controller configured to: in response to the folding detector detecting the display being folded along the folding line such that the first area and the second area face each other, control the detector to detect a user interaction through an exposure area, which is an exposed part of the second area, and the cover, and in response to the folding detector detecting the display being folded along the folding line such that two parts of the cover face each other, control the detector to detect a user interaction through the first area and the second area, wherein the controller is further configured to, in response to a telephone call request being received while the display is folded such that the first area and the second area face each other, control the display to display a UI for informing that a telephone call request is received on the exposure area (340, 2703, 2707), and accept or reject the telephone call request according to a user interaction (2705, 2711) detected on the cover (2509, 2701, 2709), wherein the user interaction is a dragging gesture or a flicking gesture. in response to the folding detector detecting the display being folded along the folding line such that the first area and the second area face each other, control the detector to detect a user interaction through an exposure area, which is an exposed part of the second area, and the cover, and in response to the folding detector detecting the display being folded along the folding line such that two parts of the cover face each other, control the detector to detect a user interaction through the first area and the second area, wherein the controller is further configured to, in response to a telephone call request being received while the display is folded such that the first area and the second area face each other, control the display to display a UI for informing that a telephone call request is received on the exposure area (340, 2703, 2707), and accept or reject the telephone call request according to a user interaction (2705, 2711) detected on the cover (2509, 2701, 2709), wherein the user interaction is a dragging gesture or a flicking gesture.