The Orthogonal Output Type Precession Motion Ball Reducer has been newly developed. The element of the reducer consists of five components; an inclined input shaft, a fixed ring, a precession motion rotor with freely rotating balls, a spherical converting rotor of the precession motion and an output ring. Especially, this converting rotor makes a precession motion around the different rotating axis, which axis is orthogonal to an input shaft. Also, the freely rotating balls are arranged on the precession motion rotor, which positions are different from the co-axial output type. In this report, the motion principle is analyzed. It is proved that the position of each ball attached on the precession motion rotor is the important parameter as like the co-axial type.