A rotation transfer mechanism includes a rotatable ring and has a
circumferential gear formed on a peripheral surface of the rotatable
ring, and a rotation transfer gear, wherein rotation of the rotatable
ring is transferred to the rotation transfer gear via engagement of the
circumferential gear with the rotation transfer gear while the rotatable
ring and the rotation transfer gear move relative to each other
throughout the entire relative movement range of the rotatable ring and
the rotation transfer gear shaft. The rotation transfer gear includes a
gear portion engaged with the circumferential gear to transfer the
rotation of the rotatable ring to the rotation transfer gear, and a
rotation limit portion having a non-circular cross-section engageable
with an outer edge of the circumferential gear to prohibit the rotation
transfer gear from rotating.