Child seat mounting structure

A child seat mounting structure in which a child seat can be easily mounted. The child seat mounting structure includes a seat (11) which is installed in a vehicle body, and which has a seatback (13), a headrest (14) which is mounted on the top of the seatback (13), and which has a through hole (30) formed therein, and a child seat (42) which is mounted on the seat (11), and which has a top tether (48) extending from the top thereof for fixing the child seat (42). The top tether (48) extends backward through the through hole (30) and beyond the seatback (13), and the end of the top tether (48) is engaged with a portion of the seat (11) or a portion (20) of the vehicle body.