An ab exercise device including a first tube member, a second tube member movable with respect to the first tube member, an elastic member resisting a downward movement of the second tube member and moving the second tube member upward with respect to the first tube member, a first and a second side part for supporting the ab exercise device respectively against a first and a second surface, the first and the second side part being arranged respectively to a first and a second side of the first tube member in an upper end of the first tube member, and a top part for pressing down the second tube member, the top part being attached to the second tube member.