An airbag unit comprising: an airbag; a cover part which covers the airbag; a fitting member which is fitted on a front side of the cover part and provided with a first locking part (32-1, 32-2) and a second locking part (32-3, 32-4); and a fastening member (50; 150) which fastens the fitting member on a back side of the cover part, the fastening member (50; 150) includes a first fastening part which is inserted in a predetermined insertion direction, from a side into the first locking part (32-1, 32-2), in a state in which the first locking part (32-1, 32-2) penetrates the cover part to a back side of the cover part, a second fastening part which is inserted in the predetermined insertion direction, from a side into the second locking part (32-3, 32-4), in a state in which the second locking part (32-3, 32-4) penetrates the cover part to the back side of the cover part, and a connecting part which connects a base end part of the first fastening part and a base end part of the second fastening part to form the fastening member (50; 150) into an approximate U-Shape with the first and second fastening parts (60, 70) extending parallel to the insertion direction, characterised in that external shapes of the first fastening part and the second fastening part are mutually different. an airbag; a cover part which covers the airbag; a fitting member which is fitted on a front side of the cover part and provided with a first locking part (32-1, 32-2) and a second locking part (32-3, 32-4); and a fastening member (50; 150) which fastens the fitting member on a back side of the cover part, the fastening member (50; 150) includes a first fastening part which is inserted in a predetermined insertion direction, from a side into the first locking part (32-1, 32-2), in a state in which the first locking part (32-1, 32-2) penetrates the cover part to a back side of the cover part, a second fastening part which is inserted in the predetermined insertion direction, from a side into the second locking part (32-3, 32-4), in a state in which the second locking part (32-3, 32-4) penetrates the cover part to the back side of the cover part, and a connecting part which connects a base end part of the first fastening part and a base end part of the second fastening part to form the fastening member (50; 150) into an approximate U-Shape with the first and second fastening parts (60, 70) extending parallel to the insertion direction, characterised in that external shapes of the first fastening part and the second fastening part are mutually different. a first fastening part which is inserted in a predetermined insertion direction, from a side into the first locking part (32-1, 32-2), in a state in which the first locking part (32-1, 32-2) penetrates the cover part to a back side of the cover part, a second fastening part which is inserted in the predetermined insertion direction, from a side into the second locking part (32-3, 32-4), in a state in which the second locking part (32-3, 32-4) penetrates the cover part to the back side of the cover part, and a connecting part which connects a base end part of the first fastening part and a base end part of the second fastening part to form the fastening member (50; 150) into an approximate U-Shape with the first and second fastening parts (60, 70) extending parallel to the insertion direction, characterised in that external shapes of the first fastening part and the second fastening part are mutually different.