FIG. 1 is a left-side elevational view of a abdominal exercise device, showing our new design; FIG. 2 is a rear elevational view of the invention; FIG. 3 is a front elevational view of the invention; FIG. 4 is a bottom plan view of the invention; FIG. 5 is a top plan view of the invention; FIG. 6 is a right-side elevational view of the invention; and, FIG. 7 is a perspective view of the invention.