To install a bearing in a stable state so that a folding door is not inclined, for easily cleaning the inside of a guide rail, in a folding door opening-closing device.

The bearing 7 fixed to the guide rail 3 rotatably supports a pivot shaft 6 of the folding door. The guide rail 3 has a recessed groove 20 for installing the bearing 7. A projection part 21 projecting toward the center of the groove 20 is extended in the longitudinal direction in the groove 20. This projection part 21 is arranged only on one side surface of opposed side surfaces of the groove 20. A width and the height of a lower side part than the projection part 21 of the bearing 7 are set substantially equal to a width of the groove 20 and the height up to an under surface of the projection part 21 from a bottom surface of the groove 20.