To provide a eccentric rocking reduction gear whose final reduction ratio and final output torque are greatly increased by increasing a reduction ratio with a driving external gear 65 and driven external gears 66.

Two driven external gears 66 each constructing a plurality of paired gear groups 67 are located at the same axial position on an input shaft, and the different paired gear groups 67 are shifted to each other in the axial direction of the input shaft 62. Thus, the two driven external gears 66 constituting the paired gear groups 67 only exist at the same axial position on the input shaft 62. As a result, the reduction ratio with the driving and driven external gears 65, 66 is easily increased without the mutual interference of the driven external gears 66 even when their diameters are increased to the utmost limit.

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