An airbag device includes an airbag, an inflator, and a mounting plate. A steering wheel includes a wheel main body and a core member as a central member. A mounting member is provided to any one of the mounting plate side and the core member side, and a locking body is provided to the other thereof. The mounting member includes a column part and a locking protrusion provided in a protruding manner to a distal end portion of the column part. The locking body is locked with an inner corner portion between the column part and the locking protrusion, whereby the airbag device is mounted to the steering wheel. A locking abutment surface of the locking protrusion, which faces a proximal end portion of the column part, includes a slip-off prevention protrusion that holds the locking body on the proximal-end-portion side of the locking protrusion.