To provide an auxiliary step allowing one to freely get on/off even when stored in a cabin without letting a step plate support member become a large obstruction in getting on/off.

The step plate 1 is provided reciprocably between a storage position X on a vehicle step S already provided in a cabin and a projection position Y at a front lower side of the vehicle step S. In the step plate 1, struts 3 are vertically standingly provided at right and left sides, each of a pair of right and left arms 5 suspending the struts 3 at the projection position Y is pivotally fitted/connected between the respective struts 3 and the vehicle step S, a bent part of a bell crank 7 is pivotally fitted to an appropriate portion of the respective arms 5, and links 8, 9 are pivotally fitted/connected between one end of the bell crank 7 and the strut 3 and between the other end of the bell crank 7 and the vehicle step S respectively. The step plate 1 is horizontally arranged at the storage position X and the projection position Y, and it is controlled so as to be reciprocated on a constant track.