A portable device and a control method thereof are disclosed that enable a user to more conveniently and accurately control a flexible display. The portable device includes a main display, a flexible display, a measurement unit configured to measure a first length of the flexible display, the first length being a measurement of the flexible display that is extended from the housing unit, when the flexible display is extended from the housing unit, and a control unit configured to obtain a second length of the flexible display, compare the second length with the width of the main display, and to display an indicator configured to indicate the second length on the main display according to the comparison result. The second length is a measurement of the flexible display that is not extended from the housing unit using the first length when the flexible display is extended from the housing unit.