A device enabling for a user to control a flexible display more convenient and precise and a controlling method therefor, are discussed. According to one embodiment disclosed for this, the device includes a flexible display, a length measuring unit configured to measure an expanded length of the flexible display expanded from the device, a speed measuring unit configured to measure a speed of which the flexible display expanded from the device and a processor configured to control the flexible display, the length measuring unit, and the speed measuring unit, wherein if the flexible display is expanded to a unit length, the processor displays an application execution screen corresponding to the unit length in the flexible display.