An airbag of a head-protecting airbag device includes a bag body, a tension belt extending from a front region of the bag body and a tether for covering an outer circumference of the bag body. The bag body includes a terminal inflatable portion and a central inflatable portion. The tension belt is disposed along a front and rear direction of the bag body so as to be deployable on an outboard side of the terminal inflatable portion. The tether is run through a slit formed on a partitioning portion which partitions the terminal inflatable portion from the central inflatable portion and covers an inboard side of the terminal inflatable portion and an outboard side of the central inflatable portion.