An image data conversion device includes an image data input unit to which image data formed of a plurality of first pixel data, each including values of three basic colors of red, green and blue, is inputted; and a color converter configured to convert first pixel data into second pixel data including at least the values of the three basic colors and a value of a fourth color, by processing each of the plurality of first pixel data forming the image data. The color converter includes a controller configured to control changes in the value of the fourth color included in the second pixel data corresponding to the first pixel data, on the basis of the values of the three basic colors included in the first pixel data.