A vehicle side airbag device comprising: an inflator that generates a gas upon activation; a side airbag (20; 70; 80; 90) that has two bag portions (34, 36; 100, 102) partitioned from one another by a partition portion (32; 92), the side airbag (20; 70; 80; 90) being inflated and deployed, when the gas is supplied to an inner side of the side airbag (20; 70; 80; 90), toward a vehicle front side from a side portion of a vehicle width direction outer side of a seat back of a vehicle seat, the two bag portions (34, 36; 100, 102) being adjacent to one another along a vehicle body side portion, and the side airbag (20; 70; 80; 90) restraining at least a shoulder, a chest and an abdomen of an occupant seated in the vehicle seat; and a tension cloth (26; 72; 82; 104) that is pulled between the two bag portions (34, 36; 100, 102), and that controls inflation of the side airbag (20; 70; 80; 90) in the direction in which the tension cloth (26; 72; 82; 104) is pulled to enlarge a vehicle width direction inflation width of the side airbag (20; 70; 80; 90), wherein in the inflated and deployed state of the side airbag (20; 70; 80; 90), the two bag portions (34, 36; 100, 102) are vertically adjacent to one another, and the tension cloth (26; 72; 82; 104) is pulled between a section, at an upper side of a center of the shoulder, of the bag portion disposed on an upper side that restrains the shoulder and the bag portion disposed on a lower side, characterized in that the tension cloth (26; 72; 82; 104) is disposed bridging the two bag portions (34, 36; 100, 102) on a vehicle width direction outer side of the side airbag (20; 70; 80; 90) in an inflated and deployed state of the side airbag (20; 70; 80; 90). an inflator that generates a gas upon activation; a side airbag (20; 70; 80; 90) that has two bag portions (34, 36; 100, 102) partitioned from one another by a partition portion (32; 92), the side airbag (20; 70; 80; 90) being inflated and deployed, when the gas is supplied to an inner side of the side airbag (20; 70; 80; 90), toward a vehicle front side from a side portion of a vehicle width direction outer side of a seat back of a vehicle seat, the two bag portions (34, 36; 100, 102) being adjacent to one another along a vehicle body side portion, and the side airbag (20; 70; 80; 90) restraining at least a shoulder, a chest and an abdomen of an occupant seated in the vehicle seat; and a tension cloth (26; 72; 82; 104) that is pulled between the two bag portions (34, 36; 100, 102), and that controls inflation of the side airbag (20; 70; 80; 90) in the direction in which the tension cloth (26; 72; 82; 104) is pulled to enlarge a vehicle width direction inflation width of the side airbag (20; 70; 80; 90), wherein in the inflated and deployed state of the side airbag (20; 70; 80; 90), the two bag portions (34, 36; 100, 102) are vertically adjacent to one another, and the tension cloth (26; 72; 82; 104) is pulled between a section, at an upper side of a center of the shoulder, of the bag portion disposed on an upper side that restrains the shoulder and the bag portion disposed on a lower side, characterized in that the tension cloth (26; 72; 82; 104) is disposed bridging the two bag portions (34, 36; 100, 102) on a vehicle width direction outer side of the side airbag (20; 70; 80; 90) in an inflated and deployed state of the side airbag (20; 70; 80; 90).