An airbag of the head-protecting airbag device according to the present invention pushes and opens a door portion in a lower edge of an airbag cover, when fed with inflation gas, and protrudes for covering side windows. An assist grip is located in an arrangement area of the airbag cover. The assist grip is secured to vehicle body together with the airbag cover at its fixing portions located in both ends of its grip portion. The airbag cover is provided around each of portions fixed to the vehicle body together with the fixing portions with a breakable portion. When pushed by the inflating airbag, the breakable portion is broken to shift a portion of the airbag cover located toward the door portion inward of the vehicle.