Side airbag device

An embodiment discloses a side airbag device including an airbag cushion that inflates with gas and deploys between a driver seat and a passenger seat and an inflator that is mounted on a mount provided in a rear end portion of the airbag cushion and is disposed inside the airbag cushion, wherein the airbag cushion includes a restraining portion disposed at a position corresponding to a shoulder of an occupant, and the restraining portion is configured to restrain movement of the occupant in a state in which the restraining portion is not inflated by the gas.