A lens position detector for detecting a position of a movable lens group in an optical axis direction includes a manual operating ring, a rotation of the manual operating ring causing the movable lens group to move in the optical axis direction; a code plate installed in a barrel; and a conductive brush fixed to the manual operating ring, the rotation of the manual operating ring causing relative rotational sliding between the conductive brush and the code plate. A surface of the code plate with which the conductive brush is in sliding contact is inclined to a plane orthogonal to the optical axis at an angle of inclination substantially equal to a lead angle of male and female screw threads engaged with each other which are formed on the manual operating ring and the ring member, respectively.