Vehicle side airbag device

A vehicle side airbag device comprising:

• an inflator that is disposed at a side section of a seatback of a vehicle seat;
• a rear bag section that inflates and deploys using gas from the inflator housed inside the rear bag section;
• a front bag section into which gas is supplied through a plurality of communication openings formed at a partitioning section between the front bag section and the rear bag section, that inflates and deploys toward a vehicle front side and a vehicle upper side of the rear bag section, and that protects a head of an occupant at a location at a vehicle upper side than the rear bag section;
• and
• a diffuser that is disposed inside the rear bag section, that houses the inflator and inflates using gas from the inflator, wherein an upper end portion of the diffuser, which is a portion at a location that inflates, pierces through an upper communication opening that is one of the plurality of communication openings and that is formed at an upper end portion of the partitioning section.