A brightness level frequency indicated on a frame basis by an input video signal is accumulated in decreasing order or increasing order of the brightness level so that an accumulated brightness level frequency is calculated for every brightness level. The brightness level corresponding to the accumulated brightness level frequency smaller by a predetermined value than any one of the accumulated brightness level frequencies indicated as maximum is regarded as an effective maximum brightness level. Based on this effective maximum brightness level, the number of sub-fields is determined for assignment to each different brightness segment region. With such a configuration, the resulting display device can lead to favorable halftone representation without causing viewers to feel something is wrong no matter what type of display images.