To provide a lens-advancing/retracting mechanism that can secure excellent position accuracy using a screw (a helicoid) is used.

The lens-advancing/retracting mechanism includes: a lens-supporting frame, an intermediate ring body, and a rotating ring, all of which are positioned concentrically in the center of an optical axis and sequentially from an inner peripheral side thereof; guiding protrusions formed on the lens-supporting frame, while being protruded radially at plural positions; a linear penetration groove formed on the intermediate ring body and guiding each of the guiding protrusions; partial male helicoids each formed on an outer peripheral surface of the plurality of guiding protrusions; and female helicoids each formed on an inner peripheral surface of the rotating ring and screwed onto the partial male helicoids. The lens-advancing/retracting mechanism has a backlash-reducing protrusion formed on the guide protrusion, the backlash-reducing protrusion reducing the backlash caused due to the mesh of the partial male helicoid and the female helicoid, by elastically engaging with the female helicoid.

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