There is provided a video signal processing method for performing predetermined signal processing on an input video signal to transmit an output video signal in a form of a specified transmission format through a video signal line including invalid bit polarity setting processing to be performed by an invalid bit polarity setting unit, wherein, when there exists an invalid bit having no data corresponding to data making up the input video signal in the specified transmission format of the output video signal, to count the number of low and high levels of gray-level data of the input video signal to compare a numerical size between the number of low levels and the number of high levels for judgment and to set a polarity of the invalid bit based on the judgment result.