An outside mirror apparatus for a coupled vehicle for improved visual confirmation of the positional relationship between the back of a coupled vehicle and the surroundings thereof. An object 9 to be detected is mounted to a frame 4F of a trailer 4 adjacent a pivotable coupling 5. A plurality of proximity sensors 8,8A,8B . . . are disposed at preset angular intervals in a frame 3F of a tractor 3 adjacent the pivotable coupling 5. These sensors 8,8A,8B . . . are arranged to correspond to the rotational orbit of the object 9. The object 9 is detected by each proximity sensor, thereby detecting an angle of bend "theta" between the tractor 3 and the trailer 4. Based on the detected result, the direction of a mirror surface 33A is able to be properly controlled.