A rotation urging mechanism includes an outer member which includes an outer raceway surface on an inner periphery thereof and is rotatable about a first axis, an inner member which includes, on an outer periphery thereof, an inner raceway surface disposed on a radially inner side of the outer raceway surface and is rotatable about the first axis, and a ball disposed rollably between the outer raceway surface and the inner raceway surface. One of the outer and inner raceway surfaces is formed about a second axis which is inclined with respect to the first axis, and the other raceway surface is formed about a third axis which is inclined with respect to the second axis and is disposed so as to cross the one raceway surface. The ball is disposed at a portion of intersection between the outer and inner raceway surfaces.