A flexible display device, comprising: a display including an expandable screen; a sensor configured to detect a size of the screen; and a controller configured to: display first information on the screen in a non-expanded state, display second information in a first expanded display area of the display according to expanding the screen, wherein the second information is information related to the first information, wherein the first information is information on an executing application, wherein the controller is further configured to: display a plurality of options on the screen for performing functions linked to the executing application, in response to an input options display command, receive a selection of a first option among the plurality of options for performing a first function linked to the executing application, display the second information in the first expanded display area of the display according to the first function in response to the screen being expanded to include the first expanded display area, and display third information in a second expanded display area of the display according to the first function in response to the screen being expanded further to include the second expanded display area, characterized in that, the first option is a move option and the first function is a move function, wherein the first information consists of a website screen from a website, and the second information consists of a service screen displaying information on at least one application provided by the website, wherein the service screen is overlapped on the website screen in the non-expanded state, and wherein the controller is further configured to move the service screen to the first expanded display area in response to the screen being expanded further to include the second expanded area if the current selected first option is the move option. a display including an expandable screen; a sensor configured to detect a size of the screen; and a controller configured to: display first information on the screen in a non-expanded state, display second information in a first expanded display area of the display according to expanding the screen, wherein the second information is information related to the first information, wherein the first information is information on an executing application, display first information on the screen in a non-expanded state, display second information in a first expanded display area of the display according to expanding the screen, wherein the second information is information related to the first information, wherein the first information is information on an executing application, wherein the controller is further configured to: display a plurality of options on the screen for performing functions linked to the executing application, in response to an input options display command, receive a selection of a first option among the plurality of options for performing a first function linked to the executing application, display the second information in the first expanded display area of the display according to the first function in response to the screen being expanded to include the first expanded display area, and display third information in a second expanded display area of the display according to the first function in response to the screen being expanded further to include the second expanded display area, display a plurality of options on the screen for performing functions linked to the executing application, in response to an input options display command, receive a selection of a first option among the plurality of options for performing a first function linked to the executing application, display the second information in the first expanded display area of the display according to the first function in response to the screen being expanded to include the first expanded display area, and display third information in a second expanded display area of the display according to the first function in response to the screen being expanded further to include the second expanded display area, characterized in that, the first option is a move option and the first function is a move function, wherein the first information consists of a website screen from a website, and the second information consists of a service screen displaying information on at least one application provided by the website, wherein the service screen is overlapped on the website screen in the non-expanded state, and wherein the controller is further configured to move the service screen to the first expanded display area in response to the screen being expanded further to include the second expanded area if the current selected first option is the move option.