There is a need to improve the insertion loss of a noise barrier without increasing the height of the barrier. The wells with different length compose a wedge-shaped noise reducing device. Typical results for the barrier with the wedge-shaped noise reducing device are presented. The device on the top of the barrier shows a property of acoustically soft surface in a predetermined frequency range. The barrier with the device shows a relatively constant insertion loss in the frequency range. To ascertain the results of numerical calculation, experimental results obtained by reduced-scale model are given. These results show the validity of numerical calculation. Numerical calculation on a road traffic noise reduction is shown.