PURPOSE: To develop an effective polishing effect with slight required driving power by providing the device with impact rotor beating blades arranged coaxially with the axis of a drum and forming these beating blades to a wave shape in their outer peripheral side.

CONSTITUTION: Both holding elements 11, 12 are provided with a shaft 17. This shaft 17 is driven by a motor 18 at a relatively higher number of revolutions and supports the impact rotor 3 within the drum 2. The impact rotor 3 is provided with at least the two, more adequately four beating blades 14 which are wave-shaped on the outer peripheral side 15. The wave-shaped outer peripheral side 15 is formed of a quarter arc of the same radius R respectively arranged as ruggedness. The beating blades 14 are advantageously coupled easily exchangeably with the impact rotor 3 by means of, for example, screwing, clamping or the like.