To achieve improvement of energy efficiency and power saving by utilizing pit sump water particular to tunnel construction to generate electric power and supplying the electric power as part of the power for the tunnel construction.

A power generating system utilizing sump water include a hydraulic power generation device 10 which generates electric power by utilizing sump water appearing in a pit during construction of a mountain tunnel, and supplies the generated power as part of the power for the tunnel construction. In this case, a turbid water treatment system 2 for clarifying pit sump water recovered during the tunnel construction is provided, and the hydraulic power generation device 10 is installed in such a manner that power generation is performed by utilizing a head drop when the water clarified by the turbid water treatment system 2 is discharged to a river.