The centrifugal separator according to the present invention includes a case (21a) that configures an outline, and a case inlet (21g) that is formed in the case (21a) and is connected to a water supply path (19) to cause water in the water supply path (19) to flow into the case (21a). The centrifugal separator further includes a case outlet (21h) that is formed in the case (21a) and is connected to the water supply path (19) to cause the water in the case (21a) to flow out to the water supply path (19), and a rotatable, hollow rotary cylinder (21b) that is provided inside the water supply path (19). The centrifugal separator further includes a rotary cylinder inlet (21e) that is formed in the rotary cylinder (21b) and causes water to flow into the rotary cylinder (21b), and a rotary cylinder outlet (21f) that is formed in the rotary cylinder (21b) and causes the water in the rotary cylinder (21b) to flow out of the rotary cylinder (21b). In the centrifugal separator, a direction in which the water flows throu
