support platform 12 by means of a lifting and pulling device in the form of a scissors type lifting table 42 the mounting platform 40 can be moved relative to the support platform 12 in the vertical direction with the aid of the scissors type lifting table 42 the mounting platform 40 has a mounting plate 44 which has a handrail 46 and forms a working platform for assembly personnel further first coupling devices 48 50 with extension arms 23 which can be moved between an inoperative position and an operative position in the horizontal direction are held on the mounting plate 44 the first coupling devices 48 50 of the mounting platform 40 are of identical design to the first coupling devices 20 and 22 of the support platform 12 in fig1 the support platform 12 assumes a position at the upper end of the first guide rails 28 a 28 b wherein said support platform is supported on the first connecting elements 26 in the vertical direction by means of the first coupling devices 20 22 and the second coupling devices 24 in fig1 the mounting platform 40 assumes a position at the upper end of the second guide rails 30 a 30 b and therefore assembly personnel who are standing on the mounting plate 44 of the mounting platform 40 can secure second connecting elements.