A portable device including a main display; a flexible display; a sensor unit configured to sense at least one of expanding of the flexible display and an input signal; and a processor configured to control the main display, the flexible display and the sensor unit, when a first page of a plurality of pages having a sequence is being displayed in the main display. The process also displays an indicator in the main display when the input signal is sensed, the indicator indicating a display direction of additional pages to be displayed when the flexible display is expanded, and indicating a forward direction or a reverse direction based on the first page as the display direction, and displays at least one additional page in the display direction indicated by the indicator when the expanding of the flexible display is sensed.