PURPOSE: To prevent the reduction of the power transmission efficiency by freely fitting the polishing block installation levers in slidable ways into an elevating guide tool and transferring the installation levers in the transverse direction by the turn of a turning member and always maintaining the favorable state of the inclined inner wall surface of a V-shaped pulley.

CONSTITUTION: An elevating guide device 10 which can rise and lower in the axial direction of the main and trailing shafts 1 and 2 is arranged, and the polishing block installation levers 9 and 9' having the polishing blocks 8 and 8' at the top edge are freely fitted in slidable ways through link plates 16, 16', 17 and 17' at the both edges of a sliding lever 15 gently inserted into a turning member 13. When the installation levers 9 and 9' are shifted in the lateral direction by the turn of the turning member 13, the polishing blocks 8 and 8' contact the inclined inner wall surfaces 3', 4', 5', and 6' of the V-shaped pulleys and polish said surfaces. Therefore, with the lapse of operation time, the reduction of the friction coefficient between the inclined inner wall surfaces 3', 4', 5', and 6' and the both edge surfaces of the V-block of a chain belt 7 is prevented, and the optimum contact state can be obtained.