1. A display system which repeatedly displays a frame in which two or more types of images are sequentially displayed on a display screen within one period of the frame by writing image data while scanning pixels on the display screen, the display system comprising: a controller which simultaneously selects two or more pixels of the display screen for a specific image among the two or more types of images, writes a same image data to the two or more selected pixels to display the specific image with a simultaneous writing method, individually selects the pixels of the display screen for images other than the specific image, and individually writes an image data to the individually selected pixels to display the images other than the specific image with a simultaneous writing method so as to control display of those images, wherein the controller has a function of executing the display with the simultaneous writing method and the display with the individual writing method sequentially and repeatedly, and reducing the writing period of the specific image within one period of the frame with the simultaneous writing method, and further, the controller has: a function of decreasing the writing frequency of the images sequentially displayed by allotting an extra time generated by making a writing period shorter, to the writing periods of the images sequentially displayed on the display screen within one frame period, or a function of increasing the brightness of the images without increasing the writing frequency of the images sequentially displayed by allotting the extra time to a period for determining brightness of the images sequentially displayed on the display screen within one frame period, or a function of decreasing the writing frequency of the images sequentially displayed and increasing the brightness of the images by allotting the extra time to both of the writing period and the period for determining the brightness of the images.