A side airbag device includes a folded-up airbag and a limitation member disposed around the airbag for constraining the airbag from protruding forward at airbag deployment. The limitation member is formed of a flexible sheet member into a band shape, and is joined to the folded-up airbag by the opposite end regions. The limitation member includes a loose region which is arranged around the folded-up airbag in such a manner as to be remote from the folded-up airbag. The loose region is disposed on a side of the folded-up airbag towards which the airbag protrudes. The loose region includes a tearable region in the region in a deployment direction of the airbag.