A wheelchair includes a seat frame having two transverse support rods, a foldable sunk-type seat module mounted on the seat frame and located between the two transverse support rods, a backrest frame having two upright support rods, and a foldable sunk-type backrest module mounted on the backrest frame and located between the two upright support rods. Thus, the backrest module may be mounted on and detached from the upright support rods of the backrest frame easily, rapidly and conveniently, and the seat module may be mounted on and detached from the horizontal support rods of the seat frame easily, rapidly and conveniently.