A thermochromatic device includes an insulating substrate, a back color layer, a color element, a heating element, a first electrode, and a second electrode. The back color layer is located on the insulating substrate. The color element is located on the back color layer and includes a transparence-changeable material. The transparence-changeable material performs a transformation between a transparent state and a nontransparent state at a phase change temperature. The heating element is located adjacent to the color element and includes a carbon nanotube structure. The first electrode and the second electrode are electrically connected to the heating element. A thermochromatic display apparatus using the thermochromatic device is also related.