In a rolling ball type two-stage low speed changer device 1, empirical formulas are obtained as a relationship between number of first, second, third and fourth lobes z1, z2, z3, z4 of a hypo-based groove 6 (8) and an epi-based groove 7 (9). The relationship is represented by z1>z2, z3>z4, z1−z2=2, z3−z4=2 and z3=n×z2×½ (n: integer), and enables to a precise and smooth rotational transmission without inviting differential slippage and incurring an irregular rotation and uneven torque transmission on an output shaft 16 within the practical usage, and reducing a thickness dimension to render a whole structure compact, achieving a high transmission efficiency without inviting a backlash, and attaining a high torque transmission with low noise.