A side airbag device with a base member for an inflator to be easily fixed thereto, and a method for manufacturing same is provided. The side airbag device includes: an airbag; an inflator configured to supply the airbag with gas; a base member configured to accommodate the airbag and the inflator, and to be fixed to a vehicle body; an outer covering member configured to cover at least a front side of the base member to form a front-facing interior surface; and a mounting bracket. The mounting bracket includes an inflator fixing portion to which the inflator is fixed and a base member fixing portion which is located in a position different from a position of the inflator fixing portion and fixed to the base member. The base member includes, at a left or right side portion thereof, a bracket fixing portion to which the mounting bracket is fixed.