To prevent a road or a road surface on a bridge from being occupied by a motor truck so as to eliminate the possibility of occurrence of traffic congestion and the need for those workers experienced in the assembly of a pipe-suspended scaffold.

This scaffold device for working on water comprises a pontoon 11 capable of being moved on water, a plurality of lift devices 12 provided on the pontoon 11, a plurality of legs 13 movably supported vertically by the lift device 12 and capable of raising the pontoon upward when it moves downward and its lower end reaches a sea bottom, a lift device 14 provided on the pontoon 11, and a working stage 15 supported so that it can be lifted by the lift device 14 at a position over the pontoon 11.