The invention relates to a guide device (4) for guiding a furniture part (2), in particular a sliding door or a folding sliding door, on a guide rail (16, 17), comprising at least one chassis (18) having at least one rotatably mounted rolling body (19, 20), and at least one connecting device (1) for connecting the at least one chassis (18) to the rolling body (19, 20), the invention relates to a guide device (4) for a furniture part (2), comprising at least one guide rail (16, 17), at least one running gear (21, 22, 23), by means of which the at least one running gear can be slidably mounted on a running track (21, 22, 23) of the guide rail (16, 17), and at least one connecting device, in particular in the form of a hinge, for connecting the guide device (4) to the furniture part (2), the at least one chassis (18) and the at least one connecting device (1) are formed as separate construction units from one another and can be connected, in particular releasably connected, to one another by means of at least one fastening device (24), the at least one fastening device (24) comprising at least one locking element (25), in which the at least one locking element (25) can be fastened to the at least one chassis (18) and the at least one connecting device (1). The at least one locking element is rotatably and slidably mounted on the at least one connecting device (1) or on the at least one chassis (18), preferably transversely to the fixing direction (26) of the at least one connecting device (1) and the at least one chassis (18).