The invention relates to an automatic heel unit (1) for a ski binding, comprising a base (7) for fitting the automatic heel unit (1) on a ski and a heel downholder (3) for holding down a ski boot in a heel region of the ski boot. The heel downholder (3) is mounted so as to be movable in relation to the base (7). The automatic heel unit (1) has a holding configuration in which the heel downholder (3) is located in a holding position and may interact with the heel region of the ski boot that is held in the ski binding in such a manner that the heel region of the ski boot is held down in a lowered position. Furthermore, the automatic heel unit (1) has a step-in configuration in which the heel downholder (3) is located in a step-in position and the heel region of the ski boot is released by the heel downholder (3). The automatic heel unit (1) comprises a heel support structure (6), which is configured separately from the heel downholder (3), for supporting, in a direction that is horizontally transverse to the ski, the heel region of the ski boot that is held in the ski binding in the holding configuration of the automatic heel unit (1).