It is determined whether or not an input video signal is a side panel signal, a letter box signal, or a full line signal. If the input video signal is a side panel signal or a letter box signal, when a multiple-picture displaying process or a reduced picture displaying process is performed, only a signal of an effective picture area is extracted. With only the signal of the effective picture area, the picture sizes are adjusted and the pictures are combined. Thus, even if an input video signal is a side panel signal or a letter box signal, the picture does not become small. In addition, when the reduced picture displaying process is performed, since a wasteful picture portion is not processed, the utilization efficiency of the screen is improved.