A rotation mechanism includes a shaft portion, a bearing portion, a protruding portion, and a stopper. The bearing portion configured to rotate with respect to a predetermined axis as a center of rotation and configured to slide relative to an outer periphery of the shaft portion. The protruding portion protrudes from the shaft portion. The stopper is integrally formed the bearing portion. The stopper faces the protruding portion. A length of the protruding portion in a direction in which the protruding portion protrudes is larger than a distance from the center of rotation to a sliding portion where the bearing portion slides relative to the outer periphery of the shaft portion.