Abstract: An airbag restraint unit for a front seat passenger aside a driver in an automotive vehicle comprises a casing having upper and lower chambers. An inflator for ejecting gas is disposed in the lower chamber of the casing. An airbag is disposed in the upper chamber of the casing to inflate and deploy upon being supplied with gas from the inflator. A mid-retainer is disposed in the casing and located between the inflator and the airbag. The casing includes a first engagement section having opposite first and second engagement surfaces inclined to gradually approach in a direction toward the airbag. First and second installation holes are formed respectively at the first and second engagement surfaces of the casing. The mid-retainer includes a second engagement section having opposite first and second engagement surfaces engaged respectively with the first and second engagement surfaces of the first engagement section of the casing.