A fly-back pulse width adjustment circuit and a method for adjusting the width of a fly-back pulse which are applied to a video signal processing unit realized as one chip are provided. The fly-back pulse width adjustment circuit is built into a video signal processing unit including a video amplifier, an on screen display unit, and a horizontal/vertical synchronous signal processing unit within the video signal processing unit realized as one chip. Moreover the fly-back pulse width adjustment circuit includes a pulse shaping unit which shapes the fly-back pulse received from the outside via an input terminal and then applies the shaped fly-back pulse to the horizontal/vertical synchronous signal processing unit, and a pulse-width adjustment unit which adjusts the width of the shaped fly-back pulse in response to a predetermined control signal, generates the horizontal blank signal having a different occurrence time from the result of the adjustment in response to a selection signal, and applies the horizontal blank signal to the video amplifier and the on screen display unit. The fly-back pulse width adjustment circuit which is provided as external components of a chip is designed to have a simple structure, and consequently it is possible to build the fly-back pulse width adjustment circuit into a video signal processing unit realized as one chip. Moreover, the width of a fly-back pulse can be adjusted by control of a microcontroller or a microcomputer, thereby applying the fly-back pulse width adjustment circuit to various monitors. In addition, the fly-back pulse width adjustment circuit can input the fly-back pulse via one terminal without an external circuit. Therefore it is easy to manufacture a printed circuit substrate with use of the fly-back pulse width adjustment circuit.