To provide a system and a method for dropping riprap and capable of efficiently constructing a riprap mound and shortening a construction period of time.

The riprap dropping system 1 is provided with both a large-sized riprap dropping opening 10a capable of dropping riprap 31 to the bottom of the water and a tremie pipe 12 in which a small-size riprap dropping opening 12a smaller than the large-sized riprap dropping opening 10a is formed.