PROBLEM TO BE SOLVED: To provide solid matter holding means which allows natural or artificial solid matters including sand gravel to be easily installed on a predetermined bottom of water at a low cost and can hold the solid matters in a water area for a long period of time while maintaining water flow around the solid matters.SOLUTION: An underwater structure A which is constructed on a bottom of water W is configured to arrange component units B in an almost reticular pattern. The component unit B comprises: an opening section 2 having an almost rectangular shape surrounded by a frame body 1 with a bottom surface 11 thereof almost contacted to the bottom of the water W and multiple elongated rod members 3 erected on a front surface 12 of the frame body 1. Natural or artificial solid matters are leveled in one or a plurality of the opening section 2 and protected from being flown out of the opening section 2 by the multiple rod members 3.
