PURPOSE: To install a rear under mirror to a roof, by holding the rear under mirror to the roof of an automobile with a back door rotatable vertically, and making the rear under mirror rotate up and down when the back door is rotated in the opening direction, and rotate downward and restore to the using position when the back door is rotated to the closing direction.

CONSTITUTION: A stay 12 is held to a bracket 13 fixed to the rear end of a roof 2 through a support pin 13a, and a mirror plate 11 is installed to the front end of the stay 12. When a back door is opened, a hinge male 4a fixed to the back door, and the first gear 21 are rotated in the direction (a) through a hinge pin 4c, and the first link rod 24 is moved downward through the second gear 22 and a pinion gear 23. As a result, the stay 12 of a mirror main body 10 is fluctuated by making the support pin 13a as the axis by the second link rod 15 and the third link rod 26, and the mirror main body 10 is retreated out of the passing scope of the back door. When the back door is closed, the stay 12 is fluctuated reversely to the lower side, and the mirror main body 10 comes back to the using position.