To provide a scum concentrator capable of efficiently separating and concentrating froth and sludge, low in equipment cost and maintenance cost and excellent in separation effect without adding a mechanical carrying out means such as froth carrying out machine.

A separated water collection pit 12 whose upper end is opened as an inducing port having a sufficiently large sectional area for inducing froth- separated water as slow current is disposed at a froth floating zone whose upper end has a prescribed volume, and a scum raw water scattering box 13 as a scum raw water scattering means is disposed at a scum raw water spraying zone having a sufficient volume for quickly reducing a flow speed of the scum raw water and also formed in a situation in which the scum raw water is sprayed to a horizontal direction and in radial as slow jet, and a separated water collecting weir 12a whose lower end is opened as an inducing port having a sufficiently large sectional area for inducing sludge separated water as slow current is disposed at a sludge settling zone having a prescribed volume.