Abstract: A back board having a main wall region and two lateral wall regions is securely attached to a rear side of a seat back. In such combination of seat back and back board, two presser elements, fixed to the rear side of seat back, are respectively in pressing contact with: one pressure receiving belt element extended between the main wall region of the back board and one of the two lateral wall regions of the back board; and another pressure receiving belt element extended between the main wall region of back board and another of the two lateral wall regions of back board. Thus, those two lateral wall regions of back board are resiliently bent or curved inwardly of the back board to close contact with respective two lateral sides of the seat back. The back board can be formed from a thin elastic material for light-weight purpose.

Abstract: A back board having a main wall region and two lateral wall regions is securely attached to a rear side of a seat back. In such combination of seat back and back bord, two presser elements, fixed to the rear side of seat back, are respectively in pressing contact with: one pressure receiving belt element extended between the main wall region of the back board and one of the two lateral wall regions of the back board; and another pressure receiving belt element extended between the main wall region of back board and another of the two lateral wall regions of back board. Thus, those two lateral wall regions of back board are resiliently bent or curved inwardly of the back board to close contact with respective two lateral sides of the seat back. The back board can be formed from a thin elastic material for light-weight purpose.