A flat panel image display unit such as a plasma display device is provided having a structure of signal input terminals that is adaptable flexibly to a plurality of different kinds of video signals. The image display unit includes a flat display panel, a display drive circuit block, an input signal circuit block connected between the display drive circuit block and an external apparatus for outputting a video signal, and an enclosure for housing the above components. The input signal circuit block includes a plurality of different kinds of board blocks provided replaceably according to a plurality of different forms of signals. A casing member is placed inside the enclosure and is provided with an insertion opening for accepting insertion of any of the board blocks. A guide rail is for positioning the board block to a predetermined position. The plurality of guide rails are provided according to the board block of a smallest unit size.