Disclosed is a flat panel display device for preventing a grid electrode from causing alignment error and being distorted due to thermal expansion and contraction. The grid electrode includes a mask portion with apertures through which electrons may pass, and fixtures arranged external to the mask portion with a predetermined margin for allowing thermal expansion and contraction of the mask portion. The fixtures are arranged symmetrical to each other up and down as well as left and right. The fixtures fix the mask portion such that the expansion and the extraction of the mask portion proceed opposite to one another.