In a head-protecting airbag device, an airbag includes an inflatable curtain portion that is deployable over an inboard side of a window and an overlap inflatable portion that overlaps with an inboard side of the inflatable curtain portion at airbag deployment. The overlap inflatable portion is so configured as to complete inflation after the inflatable curtain portion has completed inflation. The overlap inflatable portion is deployable into a generally rod shape extending at a slant relative to an up and down direction and a first end of the overlap inflatable portion communicates with the inflatable curtain portion at a vicinity of an upper edge of the inflatable curtain portion as inflated whereas a second end of the overlap inflatable portion is jointed to a lower edge of the inflatable curtain portion away from the first end in an up and down direction.