To provide a seat backrest structure which imposes excessive force neither on joints for mounting backrest poles to a seat base nor on a reclining mechanism, by absorbing external force added to the upper part of a backrest of a high back type backrest and preventing the backrest poles from the direct transmission of the external force.

An upper backrest 5 is attached to the upper part of a seat backrest body 4 in a way that it can be rotated around the almost horizontal axis form the upright position all through a reclining position, and is also provided with leaf springs 13 which give a constant pressure toward the upright position.