A liquid crystal display device comprising: a liquid crystal display panel configured to switch between two-dimensional video and three-dimensional video to selectively display one of the two-dimensional and three-dimensional video; and an illuminating device configured to supply light to the liquid crystal display panel, wherein the liquid crystal display device further comprises a control section for controlling the liquid crystal display panel and the illuminating device, wherein the control section is configured to set a scanning frequency of the illuminating device to be equal to a scanning frequency of the liquid crystal display panel; wherein the illuminating device includes illumination regions (25, 26, 27, 28) that are scan-lit as the liquid crystal display panel is scanned, and the crystal display panel is configured to, when the two-dimensional video is displayed, write respective images of the two-dimensional video in each frame, wherein the crystal display panel is configured to, when the three-dimensional video is displayed, alternatingly write images of the three-dimensional video for a viewer's left-eye and right-eye, wherein each image of the three-dimensional video is written twice in two subsequent frames in a first writing and a second writing, the control section is configured to set the scanning frequency of the liquid crystal display to differ between when the two-dimensional video is displayed and when the three-dimensional video is displayed; the control section is configured to, when the illuminating device is scan-lit while the two-dimensional video is displayed, start scan-lighting of the illuminating device between a start and an end of writing each frame, to extinguish one of the illumination regions (25, 26, 27, 28) approximately at the same time as the end of said writing of each frame, and to thereafter sequentially extinguish the rest of the illumination regions (25, 26, 27, 28), and the control section is configured to, when the illuminating device is scan-lit while the three-dimensional video is displayed, sequentially start scan-lighting the illumination regions (25, 26, 27, 28) of the illuminating device in the middle of a second writing of each frame and to extinguish the illumination regions (25, 26, 27, 28) sequentially a predetermined period after an end of the second writing of each frame so as to prevent a drop of luminance. a liquid crystal display panel configured to switch between two-dimensional video and three-dimensional video to selectively display one of the two-dimensional and three-dimensional video; and an illuminating device configured to supply light to the liquid crystal display panel, wherein the liquid crystal display device further comprises a control section for controlling the liquid crystal display panel and the illuminating device, wherein the control section is configured to set a scanning frequency of the illuminating device to be equal to a scanning frequency of the liquid crystal display panel; wherein the illuminating device includes illumination regions (25, 26, 27, 28) that are scan-lit as the liquid crystal display panel is scanned, and the crystal display panel is configured to, when the two-dimensional video is displayed, write respective images of the two-dimensional video in each frame, wherein the crystal display panel is configured to, when the three-dimensional video is displayed, alternatingly write images of the three-dimensional video for a viewer's left-eye and right-eye, wherein each image of the three-dimensional video is written twice in two subsequent frames in a first writing and a second writing, the control section is configured to set the scanning frequency of the liquid crystal display to differ between when the two-dimensional video is displayed and when the three-dimensional video is displayed; the control section is configured to, when the illuminating device is scan-lit while the two-dimensional video is displayed, start scan-lighting of the illuminating device between a start and an end of writing each frame, to extinguish one of the illumination regions (25, 26, 27, 28) approximately at the same time as the end of said writing of each frame, and to thereafter sequentially extinguish the rest of the illumination regions (25, 26, 27, 28), and the control section is configured to, when the illuminating device is scan-lit while the three-dimensional video is displayed, sequentially start scan-lighting the illumination regions (25, 26, 27, 28) of the illuminating device in the middle of a second writing of each frame and to extinguish the illumination regions (25, 26, 27, 28) sequentially a predetermined period after an end of the second writing of each frame so as to prevent a drop of luminance.