Abstract: A door assembling apparatus for use in automobile assembly having a door transport unit for conveying a door and for maintaining a hinge member of a vehicle body and a corresponding hinge member of a door loosely engaged with each other, a hinge-pin attaching unit for inserting a gib-headed hinge pin through the engaged hinge members, and a stopper for receiving a leading end of the hinge pin as being projected from and through the engaged hinge members. The leading end of the hinge pin increases in diameter through plastic deformation thereof by the contact with the stopper, and this increased diameter effectively prevents disengagement of the pin from the hinge members. With these features, the anti-disengagement operation can be effected very efficiently and conveniently through the plastic deformation of the leading end of the pin which is realized by effectively utilizing the original function of the hinge-pin attaching means, i.e. the function for causing the hinge pin to enter the hinge members.