To provide a back machining method and a back machining device for a belt sleeve, allowing efficient and precise machining by using a ultrasonic cutter for deep cutting, keeping the surface temperature of a sleeve lower to prevent ill effects on the property of a rubber and increasing a machining speed.

The sleeve 1 to be machined into a belt is mounted on a roll 2 and rotationally moved. The ultrasonic cutter 3 having contact with the outer periphery face of the sleeve 1 rolling around the outer periphery of the roll 2 is moved in parallel to the roll 2 for cutting the outer periphery face of the sleeve 1. Then, a grinding wheel 4 having contact with the outer periphery face of the sleeve 1 is moved in the same direction as the ultrasonic cutter 3 for grinding the outer periphery face of the sleeve 1.