The present disclosure relates to a plasma display device including a plasma display panel and a sheet disposed at a front surface of the plasma display panel to protect the plasma display panel from external light. The sheet includes a base unit formed with a plurality of grooves and a plurality of pattern unit lines formed on the plurality of grooves of the base unit and has a refractive index different from that of the base unit. The number of the pattern unit lines overlapped with any one of a plurality of discharge cells formed in the panel is 8 to 25. A lower end of the pattern unit lines has a width larger than an upper end of the pattern unit lines, and the upper end of the pattern unit lines is closer to the plasma display panel.