In a vehicle side airbag device, when a side airbag is inflated and deployed, a tension cloth disposed bridging an upper side bag portion and a lower side bag portion on the vehicle width direction outer side of the side airbag is pulled up and down. The vehicle width direction inflation width of the side airbag is enlarged, so the vehicle width direction shock absorbing stroke can be ensured by the small-capacity side airbag. The tension cloth functions as a reaction force surface that supports the upper side bag portion from the outer side in the vehicle width direction, so even in a vehicle in which the position of a door beltline is low, a shoulder of an occupant can be restrained at an early stage. In a case where the vehicle has rolled over, the tension cloth protects the side airbag from fragments of a door glass.