PURPOSE: To reduce the quantative change of abrasive materials mixed with medals ejected from an ejecting port by fixing a long helical plate around a rotary shaft, constituting it in the shape of a screw and forming the upper diameter of the helical plate smaller than the lower diameter.

CONSTITUTION: A helical plate 3 is fixed around a rotary shaft 13, which is vertically inserted inside a cylindrical pipe 1, and constituted in the shape of the screw and the diameter of an upper part 3a of the helical plate 3 is formed smaller than that of a lower part 3b so that the amount of abrasive material and medals ejected from an ejecting port 5 can be almost fixed. Then, a separating means 10 provided continuously to the ejecting port 5 is composed of a basket-shaped rotary drum 15 forming an opening 14 at one part of the side face, a guide-in passage 16 and guide-out passage 17 equipped with a lot of grinding member transmitting holes so as to sufficiently separate the abrasive material and the medals at a narrow place. The rotary drum 15 is provided with the opening 14 for taking in and out the mixture of the abrasive materials and the medals, and the drum 15 has a lot of abrasive material transmitting holes 20 on the circumferential face thereof and is formed in the shape of a polygonal bascket.