A seat unit includes a seat and a dining board is slidably and pivotably connected to the back of the backrest of the seat. A display device such as a flat-board computer, a table PC, or an In-Flight Entertainment device, is connected to the bottom face of the dining board. The dining board is connected with two links which are pivotably connected to the legs of the backrest so that the dining board is pivoted and positioned horizontally. The dining board has operation members on two sides thereof so as to be slidably engaged with grooves in the reception member on the backrest. The dining board can be slid and stored in the reception member and the passenger behind the backrest can operate and enjoy the In-Flight Entertainment device.