The present invention relates to a video signal processing apparatus for converting video signals based on a desired transmission system such as NTSC, PAL, MUSE or any other system so as to conform to a display unit of a desired screen system such as XGA, VGA or the like. The apparatus has a feature that it is provided with a PLL circuit for changing a sampling frequency used by an analog-to-digital converter for converting inputted video signals into digital signals in accordance with the sort of the transmission system of the video signals, and a controller for controlling picture element interpolation of the digital signals performed by a picture image magnifying circuit for magnifying the video signals horizontally and vertically, in accordance with the sort of the transmission system of the video signals.