Abstract: An air guiding device of a motor vehicle body includes a roof spoiler arranged on a rearward end of a roof of the motor vehicle body and above a rear window of the motor vehicle body. The roof spoiler includes a first spoiler portion extending along a transverse body axis (Y) and a second spoiler portion extending along a vertical body axis (Z). The roof spoiler includes an unmovable air guiding element and a movable air guiding element, which is movably received in an element opening of the unmovable air guiding element. For water drainage, the air guiding device includes a channel system, which is configured so as to receive and discharge water. The roof spoiler includes a spoiler entry opening. The channel system is configured so as to guide the water starting from the spoiler entry opening via the second spoiler portion to an environment.