To reduce cost by changing the number of revolutions of a diamond chip saw and changing the design of the saw in a device for cutting and removing unnecessary materials such as the sprue of an aluminum casting.

The device A for cutting and removing unnecessary materials such as the sprue 9 of a casting 8 comprises a rotary shaft 3, a motor 1 rotating the rotary shaft with high speed, and a disk-shaped diamond chip saw 2 which is mounted on the edge 4 of the rotary shaft 3 and rotates with high speed by the rotation of the rotary shaft 3 to cut and remove the unnecessary material 9 of the casting 8. The rigidity of the chip saw 2 is increased due to the effect of the gyro moment and the centrifugal force of the fast rotating diamond chip saw 2 itself at the speed of 6000-8000 rpm. Thus the thickness of the chip saw 2 can be reduced from 6-8 mm to 2.5 mm and the amount of the diamond chips to be used can be reduced so that the cutting cost reduction can be realized.