The display system includes a first storage unit storing standardized data composed chromaticity values and luminance values. An information acquirer acquires luminance values and chromaticity values of a visual target and luminance and chromaticity values of a background thereof. A standardization unit standardizes the chromaticity values and the luminance values of the visual target and the background based on these chromaticity values and the luminance values of the visual target and the background thereof and the standardized data stored in the first storage unit. A visual target contrast calculator calculates a contrast of a visual target to a background by measuring a distance in a color space between the visual target and the background each defined by the standardized luminance and chromaticity values. A second storage unit stores an expression defining a relation between the contrast thereof to the background and a size of the visual target.