A side airbag device, for a vehicle, includes: a folded portion housed in a side portion located at a vehicle front side of a rear end of the side airbag, the folded portion having a plurality of crease portions and portions to the front and rear of the folds at the plurality of crease portions being superimposed in the vehicle transverse direction, and a portion in which first and second crease portions, counting from a rear end portion side of the side airbag, are outwards folds that are folded towards the outer side in the vehicle transverse direction, and in which crease portions including and subsequent to a third crease portion, counting from the rear end portion side, that are also located at the vehicle front side of the folded portion, are inwards folds that are folded towards an inner side in the vehicle transverse direction.