The invention provides a settling device comprising an acoustic wave generator and an inclined settling chamber. The angle θ between the acoustic wave direction and the inclined settling chamber is greater than 0 and less than 90°. The invention also provides a concentration method and a separation method using the device. The invention can be used to concentrate or separate particles such as inorganic particles, organic particles, and biological particles, for example, mammalian cells, bacteria, yeast, algae, and plant cells. The invention exhibits technical merits such as higher efficiency, cost-effectiveness, and large-scale production.