Abstract: An improved system for fixedly mounting a case or the like box-shaped article onto the body of a motorcar is disclosed. The case is first placed on a mounting base fixedly secured to the body of motorcar by fitting a plurality of projections into holes on the mounting base and thereafter by operating a displacing device with the aid of a key the case is displaced relative to the mounting base so that the former is fixedly mounted on the latter. Each of the projections is formed with a V-shaped annular groove and each of the holes includes a larger diameter portion of which diameter is dimensioned larger than that of the projections and a smaller diameter portion formed by cutting a part of the larger diameter portion with a circle having the diameter dimensioned smaller than that of the larger diameter portion.