1. A design support device that supports designing of a GUI (graphical user interface), comprising: a hardware processor configured to operate as: an attribute information storing unit which stores, in advance, attribute information for displaying a GUI that is a display object as an animation; a drawing processing unit which, when a user inputs a drawing start command by using an input device, starts a drawing process of the GUI based on the attribute information and displays the GUI as an animation by redrawing a difference image of consecutive frames in a time series; a redrawing area displaying unit which sets a redrawing area based on an area redrawn by the drawing processing unit and displays an image representing the set redrawing area by overlapping the image on the GUI; and a target redrawing area displaying unit which measures a drawing processing time of an updated frame each time a frame of the GUI is updated by the drawing processing unit, and when the measured drawing processing time exceeds a predetermined reference processing time, calculates a target redrawing area that is drawable within the reference processing time and displays an image representing the calculated target redrawing area by overlapping the image on an excess frame that is a frame at which the drawing processing time exceeds the reference processing time, wherein the reference processing time is calculated in advance based on a drawing processing performance of hardware that executes the GUI and is a predetermined time in which the GUI can be smoothly without stuttering displayed as an animation, and the target redrawing area displaying unit calculates the target redrawing area for the updated frame in which the measured drawing processing time exceeds the predetermined reference processing time by multiplying the reference processing time by a draw processing area per unit time.