A position controller for a removable optical element in an optical system includes an advancing/retracting ring; a removable optical element holding member supported by the advancing/retracting ring and rotatable about a first rotational axis between an insertion position on the optical axis and a removed position; an insertion holder which holds the removable optical element holding member at the insertion position; a removal drive member supported by the advancing/retracting ring and rotatable about a second rotational axis between an insertion allowance position and a forced removing position; and an insertion/removal controller. A rotational radius from the second rotational axis to a contact point between the removable optical element holding member and the removal drive member is greater than a rotational radius from the first rotational axis to the contact point.