To provide a closure device for an opening such as a deck drain port to facilitate attaching and detaching work and to allow use for a long time reliably.

An upper plate 11 and a lower plate 12 are integrally fitted to the upper and lower parts of a hollow packing member 17 having elasticity. A rod 14 fixed with a handle 13 penetrates a through hole of the upper plate 11 to screw its screw part to a screw part of a screw member 15 fixed to the lower plate 12. When the handle 13 is rotated clockwise, the upper plate 11 is moved to an approaching direction, compression force is applied to the packing member 17 to be swollen, it is pressed to an internal wall of a deck drain port or the like to conduct sealing. When the handle 13 is rotated anti- clockwise, the upper and lower plates 11, 12 are moved to separating directions each other by returning force of the packing member 17, the packing 17 is returned to an initial nonswollen condition to be released from the press- engagement with the internal wall of the deck drain port.