The present invention relates to a suitcase, including a case body and a plurality of wheel assemblies. The case body has a cuboid shape and includes a front portion, a rear portion, a plurality of top cylindrical projections, at least one bottom tubular projection, and four sidewalls. The rear portion is connected to the front portion. The top cylindrical projections are on the rear portion and protrude outwardly. The bottom tubular projection is on the rear portion and protrudes outwardly in the opposite direction of the top cylindrical projections. The sidewalls surround the bottom tubular projection. There is a space between the bottom tubular projection and the sidewalls. The wheel assemblies are connected to the case body by closely engaged the wheel assemblies to the top cylindrical projections, or by closely engaged the wheel assemblies in the space.