The invention relates to a landing gear casing that comprises a longitudinal box with walls defining an inner housing (24) open at the bottom and enabling the stowage of the landing gear (20) inside the housing and the deployment thereof outside the housing, the walls of the casing separating the non-pressurised inner housing from a surrounding pressurised area (18) of the aircraft, characterised in that the casing includes a primary inner frame including: several primary transverse reinforcement arcs (26, 28) inside the housing; at least one longitudinal central reinforcement arc (30a, 30b) inside the housing; wherein the walls of the casing and the reinforcement being adapted to conform to the shapes of the landing gear (20) and the stowage/expansion mechanism (22) thereof.