Collected rainwater is led to a rainwater containing section by an inflow path. A water-permeable tube body extends vertically in the middle of a vertical pipe located immediately before a position at which the rainwater flows into the rainwater containing section. A bag-like filter having an open upper end and a closed lower end is contained in the tube body or covers an outer side of the tube body, and the bag-like filter captures dust in the rainwater while allowing the rainwater to pass through the bag-like filter. A mounting and dismounting means is provided to the vertical tube in order to dismount the tube body and the filter from the vertical pipe and to mount the tube body and the filter to the vertical pipe.