A modulation device including a substrate, a modulation unit, a data line, and a scan line is provided. The modulation unit is disposed on the substrate. The data line is disposed on the substrate and is electrically connected to the modulation unit. The scan line is disposed on the substrate, and has an overlapping area overlapping the data line and a non-overlapping area not overlapping the data line. In a first direction, the scan line has a first width in the overlapping area, and the scan line has a second width in the non-overlapping area. The first width is smaller than the second width. The modulation device of the disclosure reduces a resistance-capacitance loading.