A device for detecting a display mode of a video signal having first pixels corresponding to a first field, second pixels corresponding to a second field, and third pixels corresponding to a third field, includes a pixel converter, a measurement circuit, and a decision circuit. The pixel converter converts the second pixels to generate converted pixels. The measurement circuit generates measurement values related to differences between a converted pixel, a first pixel, and a third pixel. The decision circuit determines the display mode of the video signal according to the first, second, and third measurement values.