A headrace system 1 improving a scum generation function of the headrace distributing and supplying raw water to a sedimentation basin provided in a sewage treatment plant to contribute to energy savings in the sewage treatment plant as a whole and contribute to solving environmental problems, which is provided with a buoyant imparting means 20 configured with including an ejector 22, in a side in which the raw water of a headrace body 2 to which the raw water is supplied or in the raw water flowed into the headrace 2 to impart buoyant force to solid matters contained in the raw water, and scum removing means 4, 8, 9, 10, 40a, and 40b removing scum S floating on a water surface of the headrace body 2.