An abdominal exercise device includes two operating mechanisms and two connecting mechanisms. Each of the operating mechanisms includes an outer housing, a grip disposed at an end of the outer housing, and a rolling unit disposed at an opposite end of the outer housing. The rolling units of the operating mechanisms contact respectively two sides of the waist or hip of a user. The connecting mechanisms cooperate with the operating mechanisms to form a looped structure. Each of the connecting mechanisms includes an elastic connecting piece connected between the outer housings of the operating mechanisms, and a plurality of sliding units sleeved movably on the elastic connecting piece and movable upwardly and downwardly on the abdomen or back of the user.