A knee-protecting airbag apparatus includes an airbag folded and housed in the lower side of column cover. Airbag is attached to a housing with inflator at a position in its column cover side wall which wall is deployed toward column cover upon airbag inflation. When folded and housed in the housing, airbag is folded in such a manner as to turn a boundary region of driver's side wall and column cover side wall, which region is deployed forward of inflator at the complete inflation of airbag, in between inflator and driver's side wall to reduce the longitudinal width of airbag.