slider 15 the rail 14 of the toothed belt drive 12 extends over the entire narrow side of the folding door 2 such that the folding door 2 can be completely opened and closed a problem during the opening operation of the folding door 2 is the closed door position where the door portions 5 when seen in top view from above are arranged at an angle of 180 u00b0 with respect to each other collapsing the folding door 5 along the movement axis b could simply be made possible by using a high amount of force consequently it is advantageous to move the folding door 2 in a first phase first of all from a closed door position into a pre folded door position in the case of the pre folded door position the door portions 5 are situated at an angle of less than 180 u00b0 with respect to each other such that in a second phase the folding door 2 can be moved along the movement axis b from the pre folded door position into the open door position without using a large amount of force for the change in position from the closed door position into the pre folded door position a guiding member realized as a roller 9 is arranged on the slider 15 and a displacement element is arranged on the folding door 2 the displacement element is realized as a wedge 10 and u2014 when seen from fig1 u2014 is fastened on the left hand door portion 5 the roller 9 is moved along the movement axis b by the slider 15 it temporarily contacting the wedge.