To provide a descaling device which can be constantly installed in a bathtub, has a simple structure requiring no power source, and can efficiently remove scales floating in the vicinity of a bathwater level.

A running water port 9 is formed in the form of a through-hole in a bathtub plug 2 to be removably attached to the drain port 4 of the bathtub 3, the lower end of an extensible bellows tube 5 is jointed to the upper portion of the bathtub plug 2 in a state of surrounding the running water port 4, and a sucker 6 is provided in the upper end of the bellows tube 5. The sucker 6 has many slits 13 formed in the outside periphery, a lumen 14 communicating with the bellows tube 5, and an opening 7 opened upward of the lumen. Furthermore, a long pull-up member 8 connected to the upper portion of the bathtub plug 2 is inserted into the interior of the bellows tube 5 and pulled out of the opening 7 of the sucker 6, and the upper end of the pull-up member 8 is connected to a fixing bracket 15 provided in the upper portion of the bathtub 3.