A mounting structure of a driver airbag unit in which the driver airbag unit is attached to a steering wheel so as to be movable at least toward and away from the driver; the driver airbag unit is biased toward the driver by a biasing member; and an electric circuit (10, 11) is operated when the driver airbag unit is pressed by the driver and displaced away from the driver, the driver airbag unit including: an airbag including a folded body; an inflator for expanding the airbag; a retainer to which the airbag and the inflator are attached; a module cover attached to a driver-side face of the retainer, so as to cover the folded body of the airbag, wherein the module cover includes a main surface portion covering a driver-side face of the folded body of the airbag, and a wall portion projecting from the main surface portion in a direction away from the driver; and the retainer being attached to the steering wheel so as to be movable at least toward and away from the driver, the mounting structure of driver airbag unit comprising: a leg member projecting from the retainer in a direction away from the driver, wherein the leg member is: movable at least away from and toward the driver with respect to the retainer; connected to the steering wheel; formed separately from the retainer; and inserted from a driver side of the mounting structure through a leg insertion hole formed in the retainer, so as to be movable from and toward the driver, characterized in that the leg member includes a pair of guide plates (43, 44) projecting toward the driver; and the wall portion is inserted between the guide plates (43, 44) so as to be movable at least away from and toward the driver along the guide plates (43, 44). an airbag including a folded body; an inflator for expanding the airbag; a retainer to which the airbag and the inflator are attached; a module cover attached to a driver-side face of the retainer, so as to cover the folded body of the airbag, wherein the module cover includes a main surface portion covering a driver-side face of the folded body of the airbag, and a wall portion projecting from the main surface portion in a direction away from the driver; and the retainer being attached to the steering wheel so as to be movable at least toward and away from the driver, the mounting structure of driver airbag unit comprising: a leg member projecting from the retainer in a direction away from the driver, wherein the leg member is: movable at least away from and toward the driver with respect to the retainer; connected to the steering wheel; formed separately from the retainer; and inserted from a driver side of the mounting structure through a leg insertion hole formed in the retainer, so as to be movable from and toward the driver, characterized in that the leg member includes a pair of guide plates (43, 44) projecting toward the driver; and the wall portion is inserted between the guide plates (43, 44) so as to be movable at least away from and toward the driver along the guide plates (43, 44). a leg member projecting from the retainer in a direction away from the driver, wherein the leg member is: movable at least away from and toward the driver with respect to the retainer; connected to the steering wheel; formed separately from the retainer; and inserted from a driver side of the mounting structure through a leg insertion hole formed in the retainer, so as to be movable from and toward the driver, characterized in that movable at least away from and toward the driver with respect to the retainer; connected to the steering wheel; formed separately from the retainer; and inserted from a driver side of the mounting structure through a leg insertion hole formed in the retainer, so as to be movable from and toward the driver, characterized in that the leg member includes a pair of guide plates (43, 44) projecting toward the driver; and the wall portion is inserted between the guide plates (43, 44) so as to be movable at least away from and toward the driver along the guide plates (43, 44).