1. A caption detection device comprising: a delay unit which delays a current-frame image to output a previous-frame image; a current feature detection unit which receives the current-frame image to detect a caption feature in each region; a previous feature detection unit which receives the previous-frame image from the delay unit to detect a caption feature in each region; a caption emergence region detection unit which detects a region where the caption emerges based on a temporal change between the feature in each region of the current-frame image from the current-feature detection unit and the feature in each region of the previous-frame image from the previous feature detection unit; and a caption disappearance region detection unit which detects a region where the caption disappears based on the temporal change between the feature in each region of the current-frame image from the current feature detection unit and the feature in each region of the previous-frame image from the previous feature detection unit.