Abstract: The disclosure relates to an apparatus for assembling a seat for use in an automobile. The apparatus comprises a horizontally rotatable rotary table mounted on a base; a first supporting arm whose front end portion is longitudinally pivotally mounted on the rotary table by a first hinge axis; a second supporting arm whose rear end portion is longitudinally pivotally mounted on the rear end portion of the first supporting arm by a second hinge axis; a setting hose which is mounted on the front end portion of the second supporting arm and on which the lower corner of the seat back frame is placed in a position in which the seat back frame is approximately perpendicular to the rotary table; a rotation locking mechanism for locking the rotary table at a predetermined rotational position thereof; a first stopper which contacts with the first supporting arm so as to lock the first supporting arm in a forward position in which the first supporting arm forms an angle of approximately 45.degree.