Abstract: Upper and lower flap doors respectively hinged to an upper lintel member and to a lower sill member of a doorway frame constituting almost the entire side wall of the body of a van type motortruck to swing open respectively outwardly and upwardly to a horizontal position and outwardly and downwardly to a vertical position are intercoupled by a coupling device comprising two coupling mechanisms installed close to two posts constituting side members of the doorway frame, each coupling mechanism comprising members intercoupling the flap doors to synchronize their movements and cause gravitational forces acting thereon to counterbalance each other, thereby reducing the physical effort required for manual opening and closing of the doors.