Abstract: A rotation transmission mechanism of the invention includes an inner rotating member and an outer rotating member that is rotatably disposed with respect to the inner rotating member. The inner rotating member includes an outer peripheral protruding portion that protrudes toward an outer peripheral side. The outer rotating member includes an annular portion and an inner peripheral protruding portion. The outer peripheral protruding portion has a forward movement surface at a position shifted from a center of the outer peripheral protruding portion in a forward rotational direction in which the rotation transmission mechanism is rotated by forward movement. An elastically deformable portion is disposed between the forward movement surface and the inner peripheral protruding portion.

Abstract: Disclosed is a rotation transmission mechanism including: an internal rotation member inserted by a crankshaft of a bicycle; and an external rotation member configured on the internal rotation member. The internal rotation member includes: an internal rotation member body. The external rotation member includes: a circular ring part configured at an outer side of the outer circumferential convex parts; and inner circumferential convex parts protruding to an inner circumferential side of the circular ring part and configured alternately with the outer circumferential convex parts. Elastic deformation parts are configured between the outer circumferential convex parts and the inner circumferential convex parts on a rotation direction side of the advancing outer circumferential convex parts. The outer circumferential convex parts are formed in such a manner that a surface on the rotation direction side is greater than a surface on an opposite side of the rotation direction.