Abstract: A self-test device for a monitor which enables a user to check whether the monitor is in a normal operating state or not by displaying a self-test pattern on the screen of the monitor if the user disconnect a cable connector of the monitor from a personal computer (PC). The self-test device includes a clamp signal generating section for receiving a pulse signal having a predetermined period and for generating a first pulse signal and a second pulse signal which is a clamp signal, and a self-test signal generating section for generating R',G',B' video signals which are self-test signals for the monitor by processing the first pulse signal generated from the clamp signal generating section and for outputting the R',G',B' video signals to the video processing section which is controlled by the clamp signal generated from the clamp signal generating section.