A mirror assembly 3 is detachably attached to an open side 2a of a mirror housing 2 in an exterior rearview mirror system (exterior mirror) 1 that is mounted outside a vehicle body. A mirror 4 in the mirror assembly 3 is comprised of a transparent glass plate 5 with a reflective coating 6 spread over a back surface of the transparent glass plate 5, through which reflective coating 6 electric current passes to produce an antiglare effect. The electric current passing through the reflective coating 6 is controlled using a sensors 8, 9 that detect intensity of light from surroundings and rearward of the vehicle body, and an electronic control circuit 10 that compares intensity of light detected in each sensor 8, 9 to automatically adjust an antiglare level of reflection in the reflective coating 6. A battery 11 that is connected with the electronic control circuit 10 and supplies electric current into the reflective coating 6 is provided in the mirror housing 2.