To provide a suppression pool water purifying device capable of purifying storage water during plant operation.

Coarse solid included in storage water 9 in a suppression pool sent from the first pump 14 is separated by a liquid cyclone 15, captured with the first belt filter 27 and fine solid remaining in the water from which coarse solid is removed with a liquid cyclone 15, is captured with the second filter belt 37. Very fine solid included in the water which is sent from the second pump 18 and have transmitted the second belt filter 37 is captured with an ion exchanger demineralizer 19. The water squeezed from both belt filters 27 and 37 by a first dewatering mechanism 31 and the second dewatering mechanism 41 is stored in an exhaust tank 20 together with very fine solid contained in the water to remove the solid in the storage water in the suppression pool 8.