A unit for performing light blocking and dust proof is disclosed. The light blocking and dust proof unit is fixed to a first optical unit, and is mounted to a second optical unit. The light blocking and dust proof unit is mounted to the second optical unit so as to be movable in the optical axial direction relative to the second optical unit, and to be regulated by different regulating portions of the second optical unit between cases where the light blocking and dust proof unit is contracted and where the light blocking and dust proof unit is expanded. The size of the light blocking and dust proof unit having such a structure can be reduced.