An actuator that has a simple mechanism capable of locking a movable member, and a lens unit and a camera with the same. The actuator (10) includes a fixed member (12), a movable member (14) having a locking element (14a), a movable member supporting means (18) for supporting the movable member so as to permit the movable member to move to an arbitrary position in a plane in parallel with the fixed member, a drive mechanism (20a, 20b, 20c, 22) translating and rotating the movable member relative to the fixed member, and an engagement member (15) engaged with the locking element to lock the movable member when the movable member has been rotated to a predetermined position.