A one-way rotational transfer mechanism includes a rotary input shaft, a rotary output shaft, a clutch member, a differential rotating member, a circumferentially-uneven-width-space forming portion formed on the rotary input shaft, a torque transfer member, and an associating device. The torque transfer member wedges between the circumferentially-uneven-width-space forming portion and the clutch member while making the torque transfer member contact the clutch so that the rotary input shaft and the clutch member become integral upon rotation of the rotary input shaft. The associating device causes the clutch member to transfer torque thereof to the rotary output shaft, and the clutch member to release engagement of the rotary input shaft with the clutch member when the rotary output shaft is rotated so that a relative rotational torque greater than a predetermined torque determined by a shape of the associating device.