To provide a settlement tank configured so as to improve the quality of treated water from a flooding section.

Raw water is supplied into a feed well 12 to flow out in a radial direction from the gap between the lower end of the feed well 12 and a plate 13. After the raw water is circulated within the inside region of an upper baffle 30, it is caused to pass through the underside of the upper baffle 30 to flow in the gap between the upper baffle 30 and the inner peripheral wall of a tank 11 and subsequently floods to a trough 15. By providing a lower baffle 40 to the lower part of the gap between the upper baffle 30 and the feed well 12, a circulating flow is formed in the inner region of the upper baffle 30 even in the case where the raw water of a high temperature is supplied and even in the case where the raw water having a temperature lower than that of the water in the tank 11 is supplied to improve the quality of the treated water.