3 is closed a first slider existing in a leading end of the rear door upper supporting arm provided in an upper side of the rear door 3 is engaged with the upper guide rail 8 b for the rear door and a third slider existing in a leading end of the rear door lower supporting arm provided in a lower side of the rear door 3 is engaged with the lower guide rail for the rear door provided in the front side lower rail board 11 for the rear door in the case of opening only the rear door 3 the rear door handle 7 of the rear door 3 is first drawn out to a near side then the rear door 3 is drawn out against a spring provided in an inner portion of the rear door upper supporting arm and the rear door lower supporting arm in such a manner as to rise to the near side the rear door upper supporting arm and the rear door lower supporting arm are locked at the rising position thereafter if the rear door 3 is slid to the rear side of the vehicle body 1 a second slider in a leading end of the rear door center.