The invention relates to a cooker used in the open. The cooker comprises a foldable support and a sleeve type steaming box, wherein the support comprises a frame, two supporting legs, two supporting plates and two windproof plates, and the supporting legs and the supporting plates are arranged on the same side. The steaming box comprises a box body, a box cover and a small lunch box, a handle is hinged to the outer side of one end of the box body in the length direction, and inwards-protruding protruding edges are arranged in the middle portions of the two ends of the box body in the length direction. The bottom of the box cover is bent to the inner side so that the box cover can be buckled to the box body, one end, opposite to the handle of the box body, of the upper end face of the box cover is connected with a connecting plate in a fastened mode, and another handle is inserted in the connecting plate. Another outwards-protruding protruding edges are arranged below the two ends of the small lunch box in the length direction, the small lunch box is supported on the protruding edges of the box body through another protruding edges, a gap is reserved in the bottom of the box body, and a gap is reserved in the bottom of the small lunch box. One end of a third handle is hinged to the middle of the outer side of one end of the small lunch box in the width direction, and the other end of the third handle is buckled to the other end of the small lunch box in the width direction.