Disclosed is a signal processing device and an image display apparatus including the same. The signal processing device and the image display apparatus comprise: a first reduction unit to receive a image signal and reduce noise of the received image signal, and a second reduction unit to perform grayscale amplification based on the image signal from the first reduction unit, wherein the second reduction unit is configured to perform the grayscale amplification so that upper-limit level of grayscale of the image signal from the first reduction unit is greater than upper-limit level of grayscale of an OSD signal. Accordingly, OSD area may be uniformly displayed regardless of ambient luminance.