A side airbag device capable of restricting an occupant from moving to the inner side in the vehicle width direction while restraining the head of the occupant is inflatable and deployable in a space beside an occupant seated in a vehicle seat. The side airbag device includes an inflator configured to generate a gas and a bag-shaped airbag inflatable and deployable in response to the gas upon activation of the inflator to protect a lateral portion of the occupant. The airbag includes a torso protection portion, and a head protection portion configured to be provided above the torso protection portion and inflatable and deployable between an upper portion of a shoulder of the occupant and a lateral portion of a head of the occupant. The head protection portion is bendable at an acute angle relative to the torso protection portion in an inflated and deployed state of the airbag.