The invention relates to a frame structure body for a seat backrest. The frame structure body has a simple structure and can protect passengers from being impacted during the tailgating of vehicles. The frame structure body is characterized in that: shoulder impact absorption parts (3) are arranged on upper parts of left and right side frames (1 and 1) and protrude forwards relative to an upper frame (2) for headrest bearing; and when the rear part is crashed, loads from shoulders of the passengers are transferred to the shoulder impact absorption parts (3).