PURPOSE: To reduce the noise due to impact sounds at the time of replenishment of balls by providing a phase differentiating device which generates an approx. 180° phase difference between the reproduced sounds by a reproducing device and impact sounds.

CONSTITUTION: A reproducing device 22 is constituted of an electric amplifier 26 and speaker 27, and the power amplifier 26 amplifies an electric signal being input from a recorder 20, and reproduces the recorded impact sounds by driving the speaker 27. The speaker 27 is attached to a frame body 19, which is located on the rear side of a lamp 18, by a bracket 30, and is adjusted so that the speaker 27 emits the reproduced sound (impact sound) toward the impact sound source. A phase differentiating device 21 generates a phase difference of 180° between the reproduced sound by the reproducing device 22 and impact sounds. Then, when the reproduced sound is emitted toward a storage tank 10, which is the impact sound source of balls, the reproduced sound and impact sounds mutually counteract when the impact sounds have a fixed cycle, and the generated sound volume is uniform, and the impact sounds are drastically reduced.