The present disclosure provides a vehicle side airbag device including: a side airbag, housed inside a side support section of a vehicle seat, that inflates and deploys toward a vehicle front side upon being supplied with gas from an inflator, the side airbag including: a bag body that is formed in a bag shape; a front-rear left-right partitioning cloth that partitions the bag body into a front bag section and a rear bag section, and that partitions the rear bag section into a left and a right chamber in a row along a vehicle width direction in an inflated and deployed state of the bag body; and a tether, provided at at least one chamber of the left or the right chamber, that bears tension in the inflated and deployed state, and that restricts inflation of the at least one chamber toward the vehicle front side.