To provide a cleaning apparatus suitable for removing clogging substances trapped in a surface layer of a sand filtration layer. A cleaning apparatus equipped with drive wheels serving as a driving device configured to move across a surface of a sand filtration layer. A pump and a jet nozzle are provided as an agitation device configured to agitate a surface layer portion of the sand filtration layer only at a desired depth, and which blows the clogging substances upward into the seawater in a turbid water intake pit together with a filtration sand. A perforated pipe for suctioning turbid water, a pump, an ejector, and a discharge pipe for dilute turbid water are provided as a suction and discharge device configured to suction turbid water blown upward into seawater in the water intake pit by the agitation device, and discharge it to outside of the turbid water intake pit. Prevents clogging by performing a timely cleaning of the sand filtration layer, thereby making it possible to maintain a high-speed seawater infiltration rate for seawater. Impact on the surrounding environment is reduced, because the apparatus suctions turbid water containing clogging substances which is blown upward into the turbid water intake pit, and discharges it to outside of the system.