A multiprimary liquid crystal display device in which deteriorations in display quality caused by the coloration of a gray representation when viewed from an oblique direction are suppressed, and a signal conversion circuit for use in such a multiprimary liquid crystal display device are provided.A signal conversion circuit according to the present invention is for use in a multiprimary liquid crystal display device, the multiprimary liquid crystal display device having a pixel defined by a plurality of subpixels including a red subpixel, a green subpixel, a blue subpixel, and a yellow subpixel, and performing multicolor display by using four or more primary colors to be displayed by the plurality of subpixels, the signal conversion circuit converting an input video signal to a multiprimary signal corresponding to four or more primary colors. When a video signal for the pixel to display a gray color having a normalized luminance of no less than 0.2 and no more than 0.3 is input, the signal conversion circuit according to the present invention performs a conversion of the video signal so that, among the normalized luminances of the plurality of subpixels, the yellow subpixel has the lowest normalized luminance.