Provided are a signal processing device and an image display apparatus including the same. The signal processing device and the image display apparatus including the same include: a signal processor 170a may include an OSC processor configured to upscale an OSC having a first resolution to a second resolution greater than the first resolution; and a synthesizer configured to synthesize at least a part of an image having the second resolution and the upscaled OSD having the second resolution, and the OSD processor outputs the OSD having the second resolution, in which luminance and transparency are adjusted.