A rotary feed mechanism including gears provided on an outer peripheral surface of an inner ring, male threads on an outer peripheral surface of an inner ring, and an outer ring having female threads which .engage with the male threads of the inner ring. At least one male thread formed between the gears of the inner ring is engaged with a female thread provided on the outer ring, and at least one pinion engages with at least one of the gears, regardless of the axial position of the inner ring with respect to the outer ring. When the at least one pinion is rotated, the rotation is transmitted to the inner ring, and the inner ring is moved in an optical axis direction, with respect to the outer ring, in accordance with the engagement between the male and female threads.