A vehicle side airbag device including: a side airbag that is accommodated in a folded-up state within a side portion, which is at a vehicle transverse direction outer side at a seatback of a vehicle seat, and, at a time of a side collision, the side airbag inflating and expanding between an upper body of a vehicle occupant and a vehicle side portion, and a vehicle transverse direction inner side surface of the side airbag, which faces the vehicle occupant, sinking in toward a vehicle transverse direction outer side; and a cloth body that is disposed at a vehicle occupant side with respect to the inflated and expanded side airbag, and that spans between front and rear both end portions of the side airbag and is stretched between the front and rear both end portions, a gap being formed between the side airbag and the cloth body.