Air filter device for a motor vehicle, comprising a housing having a receiving space for a filter element, the filter element comprising a frame which surrounds a filter material of the filter element at least in regions, the frame having a first side wall and a second side wall opposite and a first and, opposite, a second transverse wall (32, 34) connecting the side walls, a first projection (26, 30, 76, 78) protruding from each side wall (20, 22) close to one of the two transverse walls (32, 34), and the housing comprising two opposite housing side walls (44, 46) which both have at least one slot (50, 52, 80, 82, 84, 86) in which the relevant first projection (26, 30, 76, 78) of each side wall (20, 22) of the filter element can be inserted into a relevant first slot end region (54, 56, 72, 74, 98, 100, 106, 108) pointing in a first direction (64, 102, 104), characterized in that a second projection (28, 76, 78) projects from each of the side walls (20, 22) close to the other of the two transverse walls (32, 34), and the housing side walls (44, 46) each have a second slot end region (72, 74, 98, 100, 106, 108), pointing counter to the first direction (64, 102, 104), in which the second projections (28, 76, 78) can be inserted, so that the filter element is located in the receiving space of the housing in its operating position, and the side walls (20, 22) being elastically deformable, so that a spacing from one another of the two projections (26, 28, 30, 76, 78) arranged on the same side wall (20, 22) can be reduced in order to bring the relevant second projections (28, 76, 78) past inwardly directed slot guide flanks (68, 70, 92, 96, 90, 94) into the second slot end region (72, 74, 98, 100, 106, 108) assigned thereto during insertion. the filter element comprising a frame which surrounds a filter material of the filter element at least in regions, the frame having a first side wall and a second side wall opposite and a first and, opposite, a second transverse wall (32, 34) connecting the side walls, a first projection (26, 30, 76, 78) protruding from each side wall (20, 22) close to one of the two transverse walls (32, 34), and the housing comprising two opposite housing side walls (44, 46) which both have at least one slot (50, 52, 80, 82, 84, 86) in which the relevant first projection (26, 30, 76, 78) of each side wall (20, 22) of the filter element can be inserted into a relevant first slot end region (54, 56, 72, 74, 98, 100, 106, 108) pointing in a first direction (64, 102, 104), characterized in that a second projection (28, 76, 78) projects from each of the side walls (20, 22) close to the other of the two transverse walls (32, 34), and the housing side walls (44, 46) each have a second slot end region (72, 74, 98, 100, 106, 108), pointing counter to the first direction (64, 102, 104), in which the second projections (28, 76, 78) can be inserted, so that the filter element is located in the receiving space of the housing in its operating position, and the side walls (20, 22) being elastically deformable, so that a spacing from one another of the two projections (26, 28, 30, 76, 78) arranged on the same side wall (20, 22) can be reduced in order to bring the relevant second projections (28, 76, 78) past inwardly directed slot guide flanks (68, 70, 92, 96, 90, 94) into the second slot end region (72, 74, 98, 100, 106, 108) assigned thereto during insertion.