We have designed new reduction gear, in which the arc tooth bevel gear is fixed on the inclined planetary gear. Making use of the shim, we can easily adjust the backlash of the reduction gear. Such basic characteristics as the noise, the torsion and the transmission efficiency of this system, with and without the backlash, are measured by changing the load torque. We find that the noise of the system under loading does not change much even when the backlash is adjusted, while the torque-angle of torsion characteristics show hysteresis loop. The transmission efficiency of the system without the backlash is appreciably lower than that with the backlash for the low load torque. As the applied load torque is increased further, the transmission efficiency of the system increases, and the efficiency without the backlash approaches to the transmission efficiency of the system with the backlash.