Speed reducer for automobile and automobile

The utility model provides a speed reducer for an automobile and the automobile. The speed reducer comprises a speed reduction box body, the input assembly comprises an input shaft and a gear arrangedon the input shaft in a sleeving mode, the rear end of the input shaft is connected with a driving source, and a limiting step extending in the circumferential direction of the input shaft is arranged on the input shaft; the first bearing and the second bearing are installed in the reduction gearbox body, the first bearing and the second bearing can be matched with the input shaft, the second bearing is closer to the gear than the first bearing, and the second bearing can move in the axial direction of the input shaft relative to the reduction gearbox body; the first limiting component is located in the reduction gearbox body and can be arranged on the input shaft in a sleeving mode, so that the front end of an inner ring of the first bearing abuts against the limiting step, and the rearend of the inner ring of t