An airbag module, comprising: a folded or rolled airbag cushion, an inflator equipped in said airbag cushion, and a housing (110; 210; 310; 410) for stowing this airbag cushion, wherein the housing (110; 210; 310; 410) has a convex polygonal shape in cross section, comprises at least a first pair of mutually opposed side surfaces and has an opening (121; 210a; 310a; 410a) on the upper side, and when the airbag cushion expands and deploys, the first pair of mutually opposed side surfaces is arranged to expand so as to separate from each other, the airbag module further comprises a cover (440; 540) covering the opening (121; 210a; 310a; 410a) and side surfaces of the housing (110; 210; 310; 410), the cover (440; 540) including an upper surface portion that covers the opening (121; 210a; 310a; 410a) of the housing (110; 210; 310; 410) is formed with a first weak portion that extends in the longitudinal direction of the upper surface portion, that is weaker than the area surrounding thereof, and that is arranged to be cleaved by the separation of the first pair of side surfaces when the airbag cushion expands and deploys, the cover (440; 540) further includes a portion that covers a second pair of mutually opposed side surfaces of the housing (110; 210; 310; 410), formed with second weak portions (464a, 464b) that respectively extend continuously from a lower part of both ends of the first weak portion, that are weaker than a surrounding areas thereof, and that are arranged to cleave subsequent to cleaving of the first weak portion, and the housing (110; 210; 310; 410) and the cover (440; 540) are each arranged to open rotationally with respect to the longitudinal axis to deploy the airbag cushion. a folded or rolled airbag cushion, an inflator equipped in said airbag cushion, and a housing (110; 210; 310; 410) for stowing this airbag cushion, wherein the housing (110; 210; 310; 410) has a convex polygonal shape in cross section, comprises at least a first pair of mutually opposed side surfaces and has an opening (121; 210a; 310a; 410a) on the upper side, and when the airbag cushion expands and deploys, the first pair of mutually opposed side surfaces is arranged to expand so as to separate from each other, the airbag module further comprises a cover (440; 540) covering the opening (121; 210a; 310a; 410a) and side surfaces of the housing (110; 210; 310; 410), the cover (440; 540) including an upper surface portion that covers the opening (121; 210a; 310a; 410a) of the housing (110; 210; 310; 410) is formed with a first weak portion that extends in the longitudinal direction of the upper surface portion, that is weaker than the area surrounding thereof, and that is arranged to be cleaved by the separation of the first pair of side surfaces when the airbag cushion expands and deploys, the cover (440; 540) further includes a portion that covers a second pair of mutually opposed side surfaces of the housing (110; 210; 310; 410), formed with second weak portions (464a, 464b) that respectively extend continuously from a lower part of both ends of the first weak portion, that are weaker than a surrounding areas thereof, and that are arranged to cleave subsequent to cleaving of the first weak portion, and the housing (110; 210; 310; 410) and the cover (440; 540) are each arranged to open rotationally with respect to the longitudinal axis to deploy the airbag cushion.