1. A pull-down signal detection apparatus comprising: a difference circuit which detects a difference between a frame of a current-frame image and a frame of a previous-frame image delayed from the current-frame image; a determination unit which determines a block in which motion is observed based on the difference; a caption detection unit including: a current feature detection unit which receives the current-frame image to detect a feature in each of regions obtained by dividing the current-frame image, a previous feature detection unit which receives the delayed previous-frame image to detect a feature in each of regions obtained by dividing the previous-frame image, a caption emergence region detection unit which detects a region where the caption emerges based on a temporal change representing how the caption feature changes with time between a predetermined region of the previous-frame image and a predetermined region of the current-frame image, the temporal change being derived from the feature in each of the regions of the current-frame image from the current-feature detection unit and the feature in each of the regions 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 representing how the caption feature changes with time between the predetermined region of the previous-frame image and the predetermined region of the current-frame image, the temporal change being derived from the feature in each of the regions of the current-frame image from the current feature detection unit and the feature in each of the regions of the previous-frame image from the previous feature detection unit; a counter which performs counting by subtracting blocks in which the caption emerges and disappears detected by the caption detection unit from blocks in which motion is observed determined by the dynamic block determination unit; a determination unit which determines a dynamic frame according to the number of counts of the counter; and a detection unit which outputs a signal indicating that a pull-down signal is detected, when the dynamic frame determined by the determination unit is a pull-down pattern.