A mirror case positioning device for holding the mirror case at least in a normal position, on one hand, and permitting the mirror case to lightly rotate between the normal position and a rest position. A first friction plate is secured on a lower face of a flange of a bracket for supporting the mirror case. A second friction plate as a resonance body is secured on an upper face of a flange of a column mounted on a support. A vibration element is mounted on the upper face of the flange of the column so as to cooperate with the second friction plate. The vibration element is operated by a supersonic generator. When the supersonic generator is not operated, the first and second friction plates contact frictionally with each other so that the mirror case is held at a desired position including the normal position. On the contrary, when the supersonic generator is operated, the second friction plate is considerably vibrated so that the fiction between both friction plates are reduced, resulting in a light rotation of the mirror case.