Seat back putting-down device, seat with seat back putting-down device and car with seat

The invention discloses a seat back putting-down device, a seat with the seat back putting-down device and a car with the seat. The seat back putting-down device comprises a fixed plate assembly, a movable plate assembly and a hook assembly, wherein the fixed plate assembly is used for being fixed to a cushion of the seat; the movable plate assembly is used for being fixed to a back of the seat, rotationally connected to the fixed plate assembly and provided with a rotary limiting pillar in a protruding mode; the hook assembly is rotationally connected to the fixed plate assembly and provided with a hook part which can be buckled with the rotary limiting pillar in a releasing mode so that forward putting-down of the back can be limited. The seat back putting-down device can realize forward putting-down of the back of the seat instead of backward putting-down, thereby meeting the requirement of single-cab cars. Compared with an existing angle regulator assembly, the seat back putting-down device is lower in production cost, is compatible with peripheral parts of the existing angle regulator assembly, and has good universality.