A cage of each of ball bearings arranged on respective outer peripheries of eccentric portions of a motor shaft has an annular base portion interposed between an inner ring and an outer ring and a plurality of partition wall portions for forming pockets together with the base portion. In a first ball bearing, part of the base portion protrudes axially outward from the inner raceway and forms an oil receiving portion that receives lubricating oil from the second rolling bearing side, at a portion around the rotation axis and axially outward of the first rolling bearing.