To provide an fall-preventive ladder for an underground structure provided with a locking function which can be easily detached, which can support and fix the ladder in a stable state at the time of erection of the ladder, and which prevents the engagement part of the ladder from coming off bacause of inner pressure or the like.

The fall-preventive ladder 1 consists of a ladder body 3, a ladder-fixing part 4, and the engagement part 5. The ladder body 3 consists of a pair of support levers 6 and a plurality of treading cross pieces 7 provided between the support levers 6. Then the ladder-fixing part 4 fixes a hand grip 14 formed at the inner radius of a receptacle 2 by straddling it, and pivots the base end part of the ladder body 3. The engagement part 5, which is engaged with a ladder-engagement seating 13 formed at the inner radius of the receptacle 2, is provided to the other end of the ladder-fixing part 4.