There are provided an airbag device and a steering wheel that can reduce the number of components and weight and allow a retainer to be easily positioned relative to an airbag cover. An airbag cover 4 includes a side wall portion 41 standing on an inner side, a recess 42 formed in an end face at almost the center of the side wall portion 41, and retaining holes 43 and 43 formed in the side wall portion 41 on both sides of the recess 42. A retainer 3 includes a first hook 31 that is fittable in the recess 42 and contactable with a bottom face 42a of the recess 42, and second hooks 32 that are contactable with inner faces 43a of the retaining holes 43. The retainer 3 is centered in a width direction by fitting the first hook 31 in the recess 42, and the side wall portion 41 is clamped in a standing direction by the first hook 31 and the second hooks 32 by contacting the first hook 31 with the recess 42 and contacting the second hooks 32 with the retaining holes 43.