A side airbag device for suppressing movement of an occupant in a vehicle collision and protecting the occupant, provided with an airbag module having an inflator stowed in a folded cushion attached to a frame of a vehicle seat, comprising: a soft cover wound around an outer periphery of the airbag module; wherein the soft cover includes: a first side part extending from the stowing portion of the inflator in the cushion along the side surface of the folded cushion on the frame side toward the front of the vehicle, a front end part extending continuously from a front end of the first side part and wound around the end part of the cushion towards the front of the vehicle, a second side part extending continuously from the front end part along a side surface of the cushion on the side opposite the frame and extending toward the rear of the vehicle, a rear end part extending continuously from the second side part and wound around a rear end part of the cushion towards the rear of the vehicle, characterized by an engaging part extending continuously from the rear end part, overlapping with a portion of the first side part, and engaged to a stud bolt of the inflator wherein - a space is included between a folded portion of the folded cushion and the first side part side of the soft cover close to the inflator and the inflator stowing portion. a soft cover wound around an outer periphery of the airbag module; wherein the soft cover includes: a first side part extending from the stowing portion of the inflator in the cushion along the side surface of the folded cushion on the frame side toward the front of the vehicle, a front end part extending continuously from a front end of the first side part and wound around the end part of the cushion towards the front of the vehicle, a second side part extending continuously from the front end part along a side surface of the cushion on the side opposite the frame and extending toward the rear of the vehicle, a rear end part extending continuously from the second side part and wound around a rear end part of the cushion towards the rear of the vehicle, characterized by an engaging part extending continuously from the rear end part, overlapping with a portion of the first side part, and engaged to a stud bolt of the inflator wherein - a space is included between a folded portion of the folded cushion and the first side part side of the soft cover close to the inflator and the inflator stowing portion. a first side part extending from the stowing portion of the inflator in the cushion along the side surface of the folded cushion on the frame side toward the front of the vehicle, a front end part extending continuously from a front end of the first side part and wound around the end part of the cushion towards the front of the vehicle, a second side part extending continuously from the front end part along a side surface of the cushion on the side opposite the frame and extending toward the rear of the vehicle, a rear end part extending continuously from the second side part and wound around a rear end part of the cushion towards the rear of the vehicle, characterized by an engaging part extending continuously from the rear end part, overlapping with a portion of the first side part, and engaged to a stud bolt of the inflator wherein - a space is included between a folded portion of the folded cushion and the first side part side of the soft cover close to the inflator and the inflator stowing portion. - a space is included between a folded portion of the folded cushion and the first side part side of the soft cover close to the inflator and the inflator stowing portion.