An interlock device includes an outer rail, an inner rail, an intermediate rail, a base, a driving member, a stop and a locking member. The base is connected to one end of the outer rail and includes a top room and a bottom room. The driving member is movable and includes a driving portion, an engaging portion and a co-moving portion. The driving portion is located in the top room and partially exposed from the top room. The engaging portion is located in the bottom room. The stop is connected to the inner rail or the intermediate rail. The locking member is connected to the co-moving portion. When the inner rail and the intermediate rail are pulled out, the driving portion is pushed by the intermediate rail and retracted into the top room. The co-moving portion is moved to shift the locking member, and the engaging portion extends from the bottom room of the base.