A side airbag apparatus includes an inflator, an airbag body that is configured to be deployed and inflated by inflation gas supplied from the inflator, and an inflated-dimension limiter arranged inside the airbag body. The inflated-dimension limiter is joined to the airbag body by a front joint portion provided at the front end of the inflated-dimension limiter. The inflated-dimension limiter is also joined, by a rear joint portion provided at the rear end of the inflated-dimension limiter, to a portion of the airbag body that is behind a section of the airbag body to which the inflated-dimension limiter is joined by the front joint portion. The dimension between the uppermost end and the lowermost end of the front joint portion is set to be different from the dimension between the uppermost end and the lowermost end of the rear joint portion.