A touch display apparatus including a light guide plate, a light emitting module, a display panel, a plurality of prism structures, an image transmission unit, and an image detector is provided. The light guide plate has a first surface, a second surface opposite to the first surface, and a light incident surface connecting the first surface and the second surface. The light emitting module includes at least one visible light source and at least one invisible light source. The prism structures are disposed between the first surface and the display panel. The image transmission unit includes a wedge portion and a light guide portion. The wedge portion is disposed between the prism structures and the display panel. The image detector is disposed beside the light guide portion for receiving the invisible light beam from the light guide portion. A backlight module is also provided.