A mirror surface angle adjusting device is provided which can be used at both left and right outer mirror devices of a vehicle. At a mirror driving unit, positional relationships between respective points (fulcrum of swinging A1 and A2, first adjusting points B1 and B2, second adjusting points C1 and C2, first mounting points D1 and D2, second mounting points E1 and E2, and third mounting points F1 and F2) are set such that the points have line symmetry with respect to 45° direction reference lines P1, P2. Accordingly, from a functional standpoint as well, there are no obstacles at a time of mounting, and as a result, a same type of mirror driving unit can be used at both a left door mirror device and a right door mirror device.