A digital video signal output device (100, 110, 120, 700) for outputting a digital video signal to an external digital video display device (200, 210, 210, 900) via a transmission interface having a predefined upper limit on its data transmission rate, wherein the digital video signal has a video-data period for transmitting video data and a blanking period, the digital video signal output device (100, 110, 120, 700) comprising: a difference detector (103, 113) configured to detect at least one rectangular area that has a predefined size, that is a portion of the entire image in a single frame of a digital video signal, and that includes a part where a difference between the entire image in a single frame of the digital video signal and the entire image one frame previous to said frame has occurred, configured to output an image of the detected at least one rectangular area as at least one cutout image (151 to 154), and configured to output cutout-area information specifying the at least one rectangular area's position within the entire image; a display capability capturer (101, 121, 701) configured to capture, from the digital video display device (200, 210, 210, 900), display capability data having described therein at least one video format of the at least one cutout image (151 to 154) in which the digital video display device (200, 210, 210, 900) is capable of displaying; and a transmitter (105, 115, 125, 703) configured to output the digital video output signal by transmitting, during the video-data period, data representing the at least one cutout image (151 to 154) encoded based on the video format captured by the display capability capturer (101, 121, 701) and superimposing and transmitting, during the blanking period of the digital video signal for the at least one rectangular area, the corresponding cutout-area information encoded based on the video format and an await frame number as timing information representing a point when the at least one cutout image (151 to 154) is to be displayed. a difference detector (103, 113) configured to detect at least one rectangular area that has a predefined size, that is a portion of the entire image in a single frame of a digital video signal, and that includes a part where a difference between the entire image in a single frame of the digital video signal and the entire image one frame previous to said frame has occurred, configured to output an image of the detected at least one rectangular area as at least one cutout image (151 to 154), and configured to output cutout-area information specifying the at least one rectangular area's position within the entire image; a display capability capturer (101, 121, 701) configured to capture, from the digital video display device (200, 210, 210, 900), display capability data having described therein at least one video format of the at least one cutout image (151 to 154) in which the digital video display device (200, 210, 210, 900) is capable of displaying; and a transmitter (105, 115, 125, 703) configured to output the digital video output signal by transmitting, during the video-data period, data representing the at least one cutout image (151 to 154) encoded based on the video format captured by the display capability capturer (101, 121, 701) and superimposing and transmitting, during the blanking period of the digital video signal for the at least one rectangular area, the corresponding cutout-area information encoded based on the video format and an await frame number as timing information representing a point when the at least one cutout image (151 to 154) is to be displayed.