To provide a horizontally sliding door device for a vault or the like, which has no bottom rail at a location between an emergency door and a floor, and can move a wagon or the like with casters without overriding any stepped hindrance between inside and outside of a safe.

According to the structure of the horizontally sliding door device which is hung and arranged in an entrance of the vault or the like, a door main body 6 slidably hung in the entrance is horizontally divided into upper and lower door bodies. Then the lower-half door body 62 is hung from the upper-half door body 61 in a laterally slidable manner, and functions as the emergency door.