device for displaying content, the device comprising: a user input unit configured to receive a setting input for reference content, wherein reference content is information to be referred to while a user views content using the device; a display configured to display content; and a controller configured to receive the setting input for the reference content while the content is displayed on the display, to display, on the display, a division line indicating division of the content; wherein: the content is included in a page that received the setting input; the controller is configured to: generate the division line by analyzing layout information of the content included in the page, to receive a selection input for selecting a part of content divided based on the division line, and to set, as the reference content, the part of content selected based on the selection input; control the display to display the reference content on a second window that is independent from a first window on which the content included in the page is displayed, wherein the controller, in response to receiving a hiding request input for the second window through the user input unit, sets a display layer of the second window to be lower than a display layer of the first window to hide the second window; and control the display to display an indicator at an edge of the first window that indicates a hidden state of the second window while the second window is completely hidden. a user input unit configured to receive a setting input for reference content, wherein reference content is information to be referred to while a user views content using the device; a display configured to display content; and a controller configured to receive the setting input for the reference content while the content is displayed on the display, to display, on the display, a division line indicating division of the content; wherein: the content is included in a page that received the setting input; the controller is configured to: generate the division line by analyzing layout information of the content included in the page, to receive a selection input for selecting a part of content divided based on the division line, and to set, as the reference content, the part of content selected based on the selection input; control the display to display the reference content on a second window that is independent from a first window on which the content included in the page is displayed, wherein the controller, in response to receiving a hiding request input for the second window through the user input unit, sets a display layer of the second window to be lower than a display layer of the first window to hide the second window; and control the display to display an indicator at an edge of the first window that indicates a hidden state of the second window while the second window is completely hidden. the content is included in a page that received the setting input; the controller is configured to: generate the division line by analyzing layout information of the content included in the page, to receive a selection input for selecting a part of content divided based on the division line, and to set, as the reference content, the part of content selected based on the selection input; control the display to display the reference content on a second window that is independent from a first window on which the content included in the page is displayed, wherein the controller, in response to receiving a hiding request input for the second window through the user input unit, sets a display layer of the second window to be lower than a display layer of the first window to hide the second window; and control the display to display an indicator at an edge of the first window that indicates a hidden state of the second window while the second window is completely hidden. generate the division line by analyzing layout information of the content included in the page, to receive a selection input for selecting a part of content divided based on the division line, and to set, as the reference content, the part of content selected based on the selection input; control the display to display the reference content on a second window that is independent from a first window on which the content included in the page is displayed, wherein the controller, in response to receiving a hiding request input for the second window through the user input unit, sets a display layer of the second window to be lower than a display layer of the first window to hide the second window; and control the display to display an indicator at an edge of the first window that indicates a hidden state of the second window while the second window is completely hidden.