To provide a waterproof device without requiring much labor in installing a waterproof plate and putting it in order.

The waterproof device arranges a pair of supports 2 erected in opposition to both side wall faces of an entrance of a building or the like, and the retractable waterproof plate 3 which is contacted on the supports 2 in erecting and is horizontal in retracting. Furthermore, a screw jack 4 retracting the waterproof plate 3 is arranged downward of the waterproof plate 3. The waterproof device is installed so that a state that the waterproof plate is retracted is at the same level as a floor face. In a normal time, passing is allowed, and during a water increase, a detachable handle 32 is fitted to a drive shaft 34 of the screw jack 4 to rotate the handle 32 so as to erect the waterproof plate 3, and contacted on watertight rubbers 14 and 16 arranged on the supports 2 to prevent the intrusion of water.