PURPOSE: To prevent the side face tensile member from becoming rugged improve accuracy of belt angle, and increase smoothness of the side face in such a way that frictional sliding sides of a V-belt is polished with a high speed rotary grinding stone.

CONSTITUTION: A belt 9 to be polished is attached to a holder 12, and a grinding stone 18 is set to orthogonally cross the belt 9. A handle 30 is turned, a nut 25 on a screw rod 24 is slid on the rod 24, and the grinding stone 18 which is operationally joined with the nut 25 is moved, so that the grinding stone can be positioned. Grinding angle of the grinding stone 18 to the belt 9 is determined in response to selected angles of a pointer 28 and an angle plate 29 with a fixing means 27, and the endless transmission belt is ground by rotationally driving the holder 12 and the grinding stone 18.