A portable device comprising: a main display configured to display a first page of a plurality of pages having a page sequence; a flexible display; a sensor unit configured to sense expanding of the flexible display and an input signal to determine a display direction of additional pages of the page sequence to be displayed when the flexible display is expanded, the input signal including at least one of a signal generated by inclination of the portable device and a touch input signal for the main display; and a processor configured to control the main display, the flexible display and the sensor unit, the processor is further configured to: display an indicator in the main display when the input signal is sensed, the indicator indicating the display direction of additional pages to be displayed when the flexible display is expanded, wherein the indicator (40-1, 40-2, 71) is displayed as an image with a plurality of pages that are folded, and the indicator (40-1, 40-2, 71) includes numbers indicating the page sequence, wherein the indicator display direction is a forward direction or a reverse direction on a basis of the first page, when the expanding of the flexible display is sensed, display at least one additional page of the plurality of pages in the main display or the flexible display in the display direction indicated by the indicator, and when the touch input signal and the signal generated by inclination of the portable device are sensed at the same time, display a preview for a second page of the plurality of pages in the main display, wherein the second page is determined by the position of the touch input signal on one of the plurality of folded pages of the indicator. a main display configured to display a first page of a plurality of pages having a page sequence; a flexible display; a sensor unit configured to sense expanding of the flexible display and an input signal to determine a display direction of additional pages of the page sequence to be displayed when the flexible display is expanded, the input signal including at least one of a signal generated by inclination of the portable device and a touch input signal for the main display; and a processor configured to control the main display, the flexible display and the sensor unit, the processor is further configured to: display an indicator in the main display when the input signal is sensed, the indicator indicating the display direction of additional pages to be displayed when the flexible display is expanded, wherein the indicator (40-1, 40-2, 71) is displayed as an image with a plurality of pages that are folded, and the indicator (40-1, 40-2, 71) includes numbers indicating the page sequence, wherein the indicator display direction is a forward direction or a reverse direction on a basis of the first page, when the expanding of the flexible display is sensed, display at least one additional page of the plurality of pages in the main display or the flexible display in the display direction indicated by the indicator, and when the touch input signal and the signal generated by inclination of the portable device are sensed at the same time, display a preview for a second page of the plurality of pages in the main display, display an indicator in the main display when the input signal is sensed, the indicator indicating the display direction of additional pages to be displayed when the flexible display is expanded, wherein the indicator (40-1, 40-2, 71) is displayed as an image with a plurality of pages that are folded, and the indicator (40-1, 40-2, 71) includes numbers indicating the page sequence, wherein the indicator display direction is a forward direction or a reverse direction on a basis of the first page, when the expanding of the flexible display is sensed, display at least one additional page of the plurality of pages in the main display or the flexible display in the display direction indicated by the indicator, and when the touch input signal and the signal generated by inclination of the portable device are sensed at the same time, display a preview for a second page of the plurality of pages in the main display, wherein the second page is determined by the position of the touch input signal on one of the plurality of folded pages of the indicator.