1. A motion vector detecting apparatus comprising: a correlation detecting unit configured to calculate difference values in a plurality of directions each between two pieces of pixel data in at least two frames and detect correlations each between two pieces of pixel data in the plurality of directions; a repetitive object detecting unit configured to detect whether or not concerned pixel data in which a motion vector is to be detected is located in a repetitive object in which pixel data representing a certain gray level or color is repeated in a certain pattern in a horizontal or vertical direction; a motion vector selecting unit configured to select a motion vector based on the difference values in the plurality of directions from the correlation detecting unit and output the selected motion vector; and a motion vector compensating unit configured to, when the repetitive object detecting unit detects that the concerned pixel data is located in the repetitive object, render a motion vector, which has been detected in a past time with respect to a motion vector newly detected from the concerned pixel data, to be easy to be output as a motion vector.