1. A three-dimensional printing device comprising: an image extractor that extracts selectively designated section from an image to be printed; an image converter that converts the designated section extracted by the image extractor into an image with a color having a higher thermal energy absorbency than section other than the designated section; a converted image printer that prints the converted image converted by the image converter onto a foaming layer surface of a thermal expansion sheet; a sheet surface raiser that applies thermal energy to the thermal expansion sheet on which the converted image is printed by the converted image printer, and causes the printed section of the converted image to expand and rise; a background color printer that prints a prescribed color that is a background color on the surface of the foaming layer surface of the thermal expansion sheet containing section raised by the sheet surface raiser; and an image printer that prints the image to be printed on the surface on which the prescribed color was printed by the background color printer.