A side airbag device for a rear seat relating to the technique of the present disclosure includes: an airbag module that is provided at an interior of a side garnish that is disposed between a vehicle body side portion and a vehicle transverse direction outer side of a seatback of a rear seat; a tubular flow regulating cloth that is provided at an interior of a side airbag of the airbag module, at a periphery of an inflator; and an airbag door that is provided at the side garnish, and that has a hinge portion and a tear portion at a periphery thereof, and that is pushed by the tubular flow regulating cloth when gas is generated from the inflator, wherein the tubular flow regulating cloth has openings at both ends thereof, and has exhaust holes in a peripheral wall thereof.