A thermal transfer printing device comprising a thermal head and a platen roll and configured to superimpose a thermal transfer sheet comprising a first colorant layer, a second colorant layer and a third colorant layer with printing paper and to deliver the thermal transfer sheet and the printing paper between the thermal head and the platen roll in such a manner that the thermal head heats the thermal transfer sheet and transfers the colorants to the printing paper to form an image thereon, wherein the thermal transfer printing device comprises: a sensor disposed between the thermal head and a supply unit configured to supply the thermal transfer sheet, applying visible light to at least two colorant layers selected from the first colorant layer, the second colorant layer and the third colorant layer, and measuring at least either of intensities of light transmitted through each of the colorant layers irradiated with the visible light and intensities of light reflected by each of the colorant layers irradiated with the visible light, or applying invisible light to at least two colorant layers selected from the first colorant layer, the second colorant layer and the third colorant layer, and measuring at least one of intensities of light transmitted through each of the colorant layers irradiated with the invisible light, intensities of light reflected by each of the colorant layers irradiated with the invisible light, and emission intensities of each of the colorant layers irradiated with the invisible light; a memory storing a table containing types of thermal transfer sheets in connection with patterns of densities or patterns of optical intensities based on the densities of at least two colorant layers selected from a first colorant layer, a second colorant layer and a third colorant layer in each type of the thermal transfer sheet, or a table containing types of thermal transfer sheets in connection with patterns of contents of an invisible light absorbing material or patterns of optical intensities based on the contents of at least two colorant layers selected from a first colorant layer, a second colorant layer and a third colorant layer in each type of the thermal transfer sheet; and an identification unit identifying the type of the thermal transfer sheet supplied from the supply unit based on measurement results from the sensor with reference to the table. a sensor disposed between the thermal head and a supply unit configured to supply the thermal transfer sheet, applying visible light to at least two colorant layers selected from the first colorant layer, the second colorant layer and the third colorant layer, and measuring at least either of intensities of light transmitted through each of the colorant layers irradiated with the visible light and intensities of light reflected by each of the colorant layers irradiated with the visible light, or applying invisible light to at least two colorant layers selected from the first colorant layer, the second colorant layer and the third colorant layer, and measuring at least one of intensities of light transmitted through each of the colorant layers irradiated with the invisible light, intensities of light reflected by each of the colorant layers irradiated with the invisible light, and emission intensities of each of the colorant layers irradiated with the invisible light; a memory storing a table containing types of thermal transfer sheets in connection with patterns of densities or patterns of optical intensities based on the densities of at least two colorant layers selected from a first colorant layer, a second colorant layer and a third colorant layer in each type of the thermal transfer sheet, or a table containing types of thermal transfer sheets in connection with patterns of contents of an invisible light absorbing material or patterns of optical intensities based on the contents of at least two colorant layers selected from a first colorant layer, a second colorant layer and a third colorant layer in each type of the thermal transfer sheet; and an identification unit identifying the type of the thermal transfer sheet supplied from the supply unit based on measurement results from the sensor with reference to the table.