The present invention relates to an apparatus for assembling a front panel, a plurality of side panels, a back panel, and a roof panel in a complete body assembly line for various vehicles. The complete body assembling apparatus realizes a new type of a coupling apparatus by which hangers for vehicle models are held in a post buck in a complete body line for a vehicle and the post buck is flexibly movable depending on the changes in various vehicle models. This in turn, allows various vehicle models to be produced in a single process by flexibly coping with various vehicle models and enhancing the efficiency of an entire complete body assembling process.