To provide a folding stairway allowing good usability by enlarging an area of a step without extending step height more than necessary.

This folding stairway 1 is disposed in a doorway 2 of a vehicle, and can transfer between a unfolding state allowing its using as a stairway and a storing state into the doorway 2 via link mechanisms 8 and 9. The link mechanism 9 is employed, so that a clearance in the longitudinal direction in a view from the upper surface is formed between a second step 4 and a third step 5 in the unfolding state. This folding stairway 1 has an auxiliary step 18 in the direction for enlarging the area of the third step 5 and narrowing the clearance between the steps 4 and 5. Support parts 19 of the auxiliary step 18 are turnably journalled to lower arms 15, and turn and move to using positions in the unfolding state and evacuating positions in the storing state.