Abstract: A clamp signal generation-control circuit includes a clamp signal controller for discriminating the existence of a sync on green signal and a separate sync signal supplied from a video card to a monitor to output a control signal according to the discrimination, and a clamp signal generator for automatically changing a generated point of the clamp signal, and a method for controlling the circuit is also provided. The generated point of the clamp signal supplied to the monitor is controlled to automatically shift the clamping position of a video signal, thereby preventing malfunction caused by a nonprofessional user's manipulation, abnormal picture display or the generation of a segment phenomenon. The circuit is adoptable to monitors supplied with various kinds of sync signals.