when said support frame is upwardly opened by a predetermined angle from {TAIL ~ the closed position} via said hinge means, said coupling shaft is pressed to the lower ends of said oblong holes while being urged by said urging means, so that said rear side frame is supported by {HEAD ~ said support frame} 
when said support frame is upwardly opened by a predetermined angle from { TAIL ~ the closed position } via said hinge means , said coupling shaft is pressed to the lower ends of said oblong holes while being urged by said urging means , so that said rear side frame is supported by { HEAD ~ said support frame }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD